In the Quran, Muhammad states clearly that no one can have real faith in God without accepting all of his judgments in all of their disputes:
Surah 4:65
65 But no, by the Lord they can have no (real) Faith until they make thee (Muhammad) judge in all disputes between them and find in their souls no resistance against thy decisions, but accept them with the fullest conviction.
So, a man comes along in the 7th century, unheralded, with no history, miracles, or verifiable prophecy, and says that no one can have real faith in God until they make him the judge of all of their affairs.
Imagine a man standing up and telling you:
Surah 4:80
80 He who obeys the Apostle obeys God: but if any turn away We have not sent thee to watch over their (evil deeds).
Yes - imagine a man telling you that when the "apostle" that he is referring to is himself. In plainer words - "If you obey me, you obey God". Elsewhere, he said exactly this in explicit terms:
Sahih al-Bukhari 2956, 2957
Narrated Abu Huraira:
That he heard Allah's Messenger (ﷺ) saying, "We are the last but will be the foremost to enter Paradise." The Prophet added, "He who obeys me, obeys Allah, and he who disobeys me, disobeys Allah.
Over and over in the Quran, obedience to God is predicated on also obeying Muhammad:
Surah 9:62
62 To you they swear by God. In order to please you: but it is more fitting that they should please God and His apostle if they are believers.
Surah 24:47
47 They say, "We believe in Allah and in the apostle, and we obey": but even after that, some of them turn away: they are not (really) Believers.
Surah 33:36
36 It is not fitting For a Believer, man or woman, When a matter has been decided By God and His Apostle, To have any option About their decision: If anyone disobeys God And His Apostle, he is indeed on a clearly wrong Path.
Whom do we have to obey if we are to get into Heaven, Muhammad?
Surah 48:17
17 No blame is there On the blind, nor is There blame on the lame, Nor on one ill (if he Joins not the war) : But he that obeys God And His Apostle,—(God) Will admit him to Gardens Beneath which rivers flow ; And he who turns back, (God) will punish him With a grievous Penalty.
Surah 4:13
13 Those are limits set by Allah. Those who obey Allah and His Messenger will be admitted to Gardens with rivers flowing beneath, to abide therein (for ever) and that will be the supreme achievement.
Who goes to Hell, Muhammad?
Surah 4:14
14 But those who disobey Allah and His Messenger and transgress His limits will be admitted to a Fire, to abide therein: And they shall have a humiliating punishment.
Surah 72:23
23 "Unless I proclaim what I receive from Allah and His Messages: for any that disobey Allah and His Messenger,- for them is Hell: they shall dwell therein for ever."
Who gets the loot when we're done fighting these people, Muhammad?
Surah 8:1
1 They ask thee concerning (things taken as) spoils of war. Say: "(such) spoils are at the disposal of God and the apostle: so fear God and keep straight the relations between yourselves: obey God and His apostle if ye do believe."
You get the point. Over and over, Muhammad tells us that in order to please God, we must obey God and His apostle (Surah 3:31-32, 4:59, 4:69, 8:20, 8:46, 9:29, 9:71, 9:84, 9:94, 24:51-52, 33:33, 33:71, 48:17, 49:1, 49:14, 58:13, 59:4, etc.).
The Muslim response is typically - "But they are only to obey Muhammad insofar as he speaks for God."
Then why doesn't he just say to obey God? Why does he set himself up over and over again as the authority, alongside God, by mentioning himself? If you equate all of your decisions and teachings with God's, you are trying to make yourself to be God to those who you're manipulating. He's telling everyone to obey God and himself, but they are getting all of their information on what "God" commands from him alone, meaning that Muhammad, a single man from the 7th century, is the sole authority.
Further, this demand for idolatrous, cultic devotion to a mere man can be evidenced by narrations like the following:
Sahih al-Bukhari 15
Narrated Anas:
The Prophet (ﷺ) said "None of you will have faith till he loves me more than his father, his children and all mankind."
Again, a man shows up in the 7th century, and says that no one can have real faith in God until they love him more than their own family, and anyone else on earth. Muhammad's repeated claims to be just a messenger (Surah 11:12, 13:7, etc.) are contradicted by his elevating of himself to the position of God on earth, whom we are to love with all of our heart, and obey unquestioningly.
The word Muslim means "submitter/one who submits". Islam means "submission". The truth is, Islam is submission not to God, but to a single Arabian man from the 7th century named Muhammad.
Next, let's see why submission to Muhammad may not be such a good idea. Let's examine this man whom we are to obey as we would God Himself.
First, notice the very convenient revelation Muhammad receives from Allah in Surah 33:
Surah 33:50
50 O Prophet! We have Made lawful to thee Thy wives to whom thou Hast paid their dowers; And those whom thy Right hand possesses out of The prisoners of war whom God has assigned to thee; And daughters of thy paternal Uncles and aunts, and daughters Of thy maternal uncles And aunts, who migrated (From Mecca) with thee; And any believing woman Who dedicates her soul To the Prophet if the Prophet Wishes to wed her; — this Only for thee, and not For the Believers (at large); We know what We have Appointed for them as to Their wives and the captives Whom their right hands Possess; — in order that There should be no difficulty For thee. And God is Oft-Forgiving, Most Merciful.
Yes, Muhammad wants you to believe that God took time in His eternal revelation to mankind to tell "the prophet" that he, and only he, can exceed the 4-wife limit, and marry as many of the believers' women as he wants. Who thinks this is legitimate?
In the same chapter, Allah abolishes adoption so that Muhammad can marry the wife (Zaynab bint-Jahsh) of his adopted son Zaid (verses 4-5, 37), and also tells the believers not to annoy Muhammad by staying too late at his house after dinner:
Surah 33:53
53 O believers! Do not enter the homes of the Prophet without permission ˹and if invited˺ for a meal, do not ˹come too early and˺ linger until the meal is ready. But if you are invited, then enter ˹on time˺. Once you have eaten, then go on your way, and do not stay for casual talk. Such behaviour is truly annoying to the Prophet, yet he is too shy to ask you to leave. But Allah is never shy of the truth. And when you ˹believers˺ ask his wives for something, ask them from behind a barrier. This is purer for your hearts and theirs. And it is not right for you to annoy the Messenger of Allah, nor ever marry his wives after him. This would certainly be a major offence in the sight of Allah.
The above is absurd, and is plainly something that came from Muhammad's own mind, whether he knew it or not. Sahih al-Bukhari 4791 chronicles the event that caused this verse to be "revealed". Also, notice in the above verse how none can marry his wives after he dies, another exception conspicuously granted for him alone (Surah 2:234).
Similarly, Muhammad also revealed that God, in His eternal words to mankind, told everyone to not speak too loud around "the prophet", and wait until he comes outside to ask him questions:
Surah 49:1-5
1 O believers! Do not proceed ˹in any matter˺ before ˹a decree from˺ Allah and His Messenger. And fear Allah. Surely Allah is All-Hearing, All-Knowing.
2 O believers! Do not raise your voices above the voice of the Prophet, nor speak loudly to him as you do to one another, or your deeds will become void while you are unaware.
3 Indeed, those who lower their voices in the presence of Allah’s Messenger are the ones whose hearts Allah has refined for righteousness. They will have forgiveness and a great reward.
4 Indeed, most of those who call out to you ˹O Prophet˺ from outside ˹your˺ private quarters have no understanding ˹of manners˺.
5 Had they been patient until you could come out to them, it would have certainly been better for them. And Allah is All-Forgiving, Most Merciful.
God also "revealed" that anyone who hurts Muhammad's feelings by saying things like "He listens to anyone", will go to Hell (Surah 9:61). A striking amount of God's eternal word to mankind deals with the personal life and pet-peeves of the one delivering the message.
In addition, Muhammad claimed that he received a dream in which an angel presented a 6 year-old girl named Aisha to him as his bride (Sahih al-Bukhari 7012), and as a result, Muhammad had intercourse with a 9 year-old girl when he was 54 years-old:
Sahih al-Bukhari 5134
Narrated `Aisha:
That the Prophet (ﷺ) married her when she was six years old and he consummated his marriage when she was nine years old. Hisham said: I have been informed that `Aisha remained with the Prophet (ﷺ) for nine years (i.e. till his death).
Above is repulsive, which is why many Muslims try to hide this fact of history. We are to believe that the man who we are to unquestioningly obey as if he were God, the successor to Jesus Christ, was the type of man who would marry a dozen women, and sleep with nine year-olds when he was over fifty.
The fact that she was nine years old is well-attested to in the six canonical Hadith collections. All of them except Jami at-Tirmidhi mention Aisha's age, and they are unanimous in the fact that she was nine years old when they consummated the marriage. The references are:
Aisha was the daughter of Abu Bakr, Muhammad's closest companion and the First Caliph. Initially, he was seemed reluctant to give her to Muhammad, with Muhammad merely responding that she was lawful for him:
Sahih al-Bukhari 5081
Narrated 'Urwa:
The Prophet (ﷺ) asked Abu Bakr for `Aisha's hand in marriage. Abu Bakr said "But I am your brother." The Prophet (ﷺ) said, "You are my brother in Allah's religion and His Book, but she (Aisha) is lawful for me to marry."
So, Abu Bakr relented, and gave Aisha to him. We are to believe that this was all the will of God, and not a companion of Muhammad compromising basic human decency to remain in Muhammad's good graces, even if that meant giving a 6 year-old in marriage to someone old enough to be her grandfather.
Muhammad tried to establish himself as continuing the revelations already revealed to mankind through the prophets in the Bible. As a result, the Quran affirms both the Old and New Testament as being inspired by God:
Surah 5:68
68 Say: "O People of the Book! ye have no ground to stand upon unless ye stand fast by the Law, the Gospel, and all the revelation that has come to you from your Lord.” It is the revelation that cometh to thee from thy Lord that increaseth in most of them their obstinate rebellion and blasphemy. But sorrow thou not over (these) people without Faith.
Above, Muhammad says that we have "no ground to stand upon" unless we stand on the Law and Gospel. This means that we must currently have both, otherwise, the basis for our foundation, and the foundation of Islam, is gone, according to Muhammad, and we have been issued a command which is impossible to fulfill - or even dangerous to attempt, if the Bible has been corrupted.
We are told in the Quran to judge by the Torah and the Gospel, and they are said to be revealed by God:
Surah 5:43-47
43 But why do they come to you for judgment when they ˹already˺ have the Torah containing Allah’s judgment, then they turn away after all? They are not ˹true˺ believers.
44 Indeed, We revealed the Torah, containing guidance and light, by which the prophets, who submitted themselves to Allah, made judgments for Jews. So too did the rabbis and scholars judge according to Allah’s Book, with which they were entrusted and of which they were made keepers. So do not fear the people; fear Me! Nor trade my revelations for a fleeting gain. And those who do not judge by what Allah has revealed are ˹truly˺ the disbelievers.
45 We ordained for them in the Torah, “A life for a life, an eye for an eye, a nose for a nose, an ear for an ear, a tooth for a tooth—and for wounds equal retaliation.” But whoever waives it charitably, it will be atonement for them. And those who do not judge by what Allah has revealed are ˹truly˺ the wrongdoers.
46 Then in the footsteps of the prophets, We sent Jesus, son of Mary, confirming the Torah revealed before him. And We gave him the Gospel containing guidance and light and confirming what was revealed in the Torah - a guide and a lesson to the God-fearing.
47 So let the people of the Gospel judge by what Allah has revealed in it. And those who do not judge by what Allah has revealed are ˹truly˺ the rebellious.
In verse 43 above, the Quran teaches that the Jews currently have the Torah that God sent, which is why they can use it to judge. In verse 45, Muhammad references Exodus 21:23-25, Leviticus 24:19-20, and Deuteronomy 19:19-21 as they appear in the current Torah, as an example for what we are to judge by. He then says the Gospel confirmed the Torah, and we are commanded to judge by it as well, which would be impossible if we didn't have it.
Also, in Surah 3, the Law and the Gospel are said to be a guide to mankind, sent down by God:
Surah 3:3-4
3 He has revealed to you ˹O Prophet˺ the Book in truth, confirming what came before it, as He revealed the Torah and the Gospel
4 previously, as a guide for people, and ˹also˺ revealed the Standard ˹to distinguish between right and wrong˺. Surely those who reject Allah’s revelations will suffer a severe torment. For Allah is Almighty, capable of punishment.
The Quran is replete with statements that establish the Christian and Jewish Scriptures as being authentic revelation from God (Surah 2:40-41, 2:53, 2:63, 2:87, 2:89, 2:97, 2:101, 2:136, 3:20, 3:48, 3:50, 3:81, 3:84, 3:119, 3:186-187, 4:47, 4:51, 4:54, 4:131, 4:136, etc. etc.). A large portion of the Quran consists of Muhammad retelling stories from the Bible, and exalting the characters from the Bible.
We also read in the Quran that "none can change God's words" (Surah 6:115, 18:27), meaning that since God sent down the Law and the Gospel, they are guaranteed to be unaltered. Further, we are told that Allah was with the original Christians, and ensured that they prevailed over their adversaries (Surah 61:14), and will elevate them until the day of resurrection (Surah 3:55). Further still, Muhammad himself is instructed to ask the Jews and the Christians if he has any doubt about his revelations (Surah 10:94).
In the Hadith, also, we get the backstory of Surah 5:43 above, where Muhammad appealed to a copy of the Torah that some Jews had in order to determine the punishment for adultery (Sahih al-Bukhari 3635, Sahih Muslim 1699a-c, etc.), meaning that he recognized the Scripture they had at that time as legitimate. He also stated that the Torah and Gospel were with the Jews and the Christians at that time (Jami at-Tirmidhi 2653).
There are also many more positive references to the Bible in the Hadith (Sahih Muslim 2713a, Jami at-Tirmidhi 3400, Sunan abu-Dawud 4449, 4736, etc.), including the statement that God wrote the Torah with His own hand (Sahih al-Bukhari 6614, Sahih Muslim 2652a).
Muslims today, however, in spite of all of this, desperately claim that the Bible has been completely corrupted, because Muhammad utterly contradicts the teaching of the Bible at every turn. Did you know, oh ignorant Christian, that the Biblical account (the same account that he was telling people to check him with, but ignore that for now) is actually all wrong?
Here are the real facts:
Don't worry though - Christians, who have always believed these doctrines as taught in the Bible, will be fine on Judgement Day and receive their due reward (Surah 2:62, 5:69), no wait - they actually won't be accepted by God, they are the worst of creatures (Surah 3:85, 98:6).
Muhammad goes so far as to claim that Jesus prophesied of him by name (Surah 61:6), and that references to him are found in the Old and New Testaments - which he acknowledges that they had in their possession:
Surah 7:157
157 Those who follow the Messenger, the Unlettered Prophet, whom they find mentioned in the Torah and the Gospel in their possession. He directs them to righteousness, and deters them from evil, ...
Of course, there is no such reference. The Muslim attempts to squeeze Muhammad into the Bible are downright dishonest and pathetic. The two most common verses that they try to make about Muhammad are Deuteronomy 18:18 (fulfilled in Jesus Christ according to Acts 3:22-26, 7:37, 7:52), and John 14:16, which is obviously in reference to the Holy Spirit, and is also a verse in which Jesus calls God "The Father", which no Muslim believes anyway (see above).
At this point though, why would it matter if the Bible prophesied of him when they contradict each other a thousand times? If the Bible has been allowed to become that corrupted, why do they even bother?
Yet, coming back to reality, we know for a fact they weren't corrupted. There are multiple existing manuscripts composing the entire Bible from during and before the time of Muhammad, the very same Bible that he was telling people was sent from God, was a guide to mankind, and prophesied of him. And besides these, there are thousands of verses quoted in early Christian writers - we have 10+ volumes of Ante-Nicene writers alone - who lived hundreds of years before Muhammad, and wrote in many different languages, in many different locations. There were also entire translations of the Bible that predate Muhammad, and by his time, had already spread to the ends of the earth. All of these sources match, and corroborate, what we have in the Bible today. Where's the evidence of all of this corruption, Muslims?
Many of the hundreds of local groups that historically have had Scripture bitterly disagreed with each other, have been separated by thousands of miles, and have never been united by a single ruling authority - for example, the Jews and Christians. So, the idea of a universal collaboration to corrupt Scripture is historically impossible, and ridiculous to the point of simple denial of reality. And, this corruption would have needed to occur after the time of Muhammad, or else dozens of passages in the Quran and Hadith are rendered complete lies.
Further, it's not like ten changes would've had to take place, tens of thousands of changes would've had to take place. And yet we know for a fact that they didn't. So unless Muhammad was affirming and appealing to a corrupt book filled with lies and deceit, you have to admit that he was a false prophet. Not once in the Quran does Muhammad make a statement about the Christian and Jewish Scriptures that would give any negative impression or warning that they are corrupt, or tampered with, or missing. Every single mention without exception is one of affirmation, or is him appealing to them for authority.
Muslims only have to claim it was corrupted or lost because when people actually went to check his claims, they found that what he taught was totally different from the Bible. That should have indicated to any honest seeker of truth that Muhammad was totally ignorant of the tradition that he was professing to affirm, and was, in reality, a false prophet, who was not continuing in that tradition at all. It's a much compelling view than the idea that God allowed every single last copy of His previous Word to mankind to be gathered up and corrupted, or lost completely, all while puzzlingly telling us, at least twice in the Quran, that "none can alter His words" (Surah 6:115, 18:27), and commanding us to judge by those revelations repeatedly.
This is in contrast to Jesus Christ, who claimed to affirm and fulfill the Old Testament (Matthew 5:17, John 5:39), actually did so, and no one ever had to claim that the Old Testament was "lost" or "corrupted" because what He taught didn't actually affirm it when people went to check. He affirmed the Old Testament that we can read today and verify, in contrast to the liar Muhammad, who according to Muslims, affirmed a "Bible" which no one has ever seen or can verify, making all his assertions of confirmation absolutely meaningless. Unlike Jesus, who has the testimony of the Law and the prophets, Muslims have to overthrow the testimony of the Law and the prophets in favor of the testimony of a single man.
Anyone who studies this issue can also see that the Old Testament and New Testament are intimately related. The New Testament is prophesied in the Old Testament (Jeremiah 31:31-34), and Jews - even Jews that rejected Jesus - were anticipating a Messiah, likewise prophesied since the very beginning of the Old Testament. When Jesus came on the scene, there was not a dispute over whether a Messiah was coming, but only over whether it was Jesus (John 7:31, 10:24, etc.). In the New Testament, there are over 250 quotations from the Old Testament, and figure after figure finds its fulfillment in the New Testament in a meaningful way. We treasure the Old Testament, value it for its prophecies and pictures of Christ, and affirm every word of it.
Contrast that intimate relationship with the vast chasm between the Bible and the Quran. The Quran doesn't affirm either the Old or New Testament at all. It doesn't carry on the theme of covenants, atonement, priesthood, or many other grand themes shared between the Old and New Testaments. This vital topic is discussed in its own article here.
And, where were all the Christians waiting for another prophet after Jesus, in like manner as the Jews were waiting for a Messiah? There aren't any, because nothing in the New Testament hints that there is any room for anyone after the Lord Jesus, and it explicitly warns us about someone exactly like Muhammad coming along (Galatians 1:6-9).
Finally, recognize that anyone, at any point in time, could do what Muhammad did. Today, I could claim that I am a prophet, that Moses, Jesus, and Muhammad all agreed with me, and prophesied of me, and that you will all go to Hell unless you obey everything I say and reveal. And, if anyone ever points out that the Bible and Quran say nothing of me, and totally contradict me, my followers, centuries later, can say that I am the final Prophet, and only my revelation must be trusted. Islam dies on this point, precisely because it's an ahistorical, new religion, which fails the biggest test that it ever hazarded to give itself - the test of historical confirmation from other prophets.
In conclusion, a man shows up unheralded and unprophesied (his lying, unverifiable claims notwithstanding), tells us we have to obey him as God or go to Hell, is a deviant sinner himself (Surah 40:55, 47:19, 48:1-2, Sahih al-Bukhari 6307), and claims to be the final prophet in a long line of prophets, but contradicts all of his predecessors at every point, and claims to affirm scriptures that he contradicts in literally thousands of verses. Those reasons, among many, many others are why I'm not a Muslim.