Muhammad believed not only that he was the last prophet, but that the Last Hour, which is a Muslim term denoting the end of the current world, was quickly to come. As a matter of fact, this was a motif of his preaching in the Quran (Surah 15:3, 16:77, 21:1, 26:6, 54:1, 78:40):
Surah 53:57
57 The approaching ˹Hour˺ has drawn near.
Repeatedly, he portrayed himself as preceding the Last Hour closely, as if he were an index finger, and the Last Hour were the middle finger:
Sahih al-Bukhari 4936
Narrated Sahl bin Sa`d As-Sa`idi:
Allah's Messenger (ﷺ), holding out his middle and index fingers, said, "My advent and the Hour's are like this (or like these)," namely, the period between his era and the Hour is like the distance between those two fingers, i.e., very short.
This is also narrated in Sahih al-Bukhari 5301, 6503-05, Sahih Muslim 867a, 2950, 2951b-e, Sunan Ibn Majah 45, 4040, and Jami at-Tirmidhi 2214.
Similarly, he speculated that the Dajjal - a figure who will be defeated by Jesus Christ immediately preceding the Last Hour - could have been a boy named Ibn Sayyad, who was a comtemporary with him. This is covered in its own article here.
These things indicate that he thought the Last Hour was very close at hand, but we can look at other narrations to get an even tighter time bound.
In Sahih Muslim, Muhammad responded to a question about the Last Hour by stating that it's going to be within the lifespan of someone who had already been born:
Sahih Muslim 2953a
Anas reported that a person asked Allah's Messenger (ﷺ) as to when the Last Hour would come. He had in his presence a young boy of the Ansar who was called Muhammad. Allah's Messenger (ﷺ) said:
If this young boy lives, he may not grow very old till (he would see) the Last Hour coming to you.
This Hadith is also narrated in Sahih Muslim 2952, 2953b-c.
Of course, this had to be reinterpreted rather early in Islamic history when the prophecy didn't come to pass, and now this passage is portrayed as speaking to the "Final Hour" for the people present when he was speaking (i.e. their death).
A few points:
While of course no Muslim will admit it, he was totally wrong about this prophecy, and is therefore a false prophet.
Another time, as we read in Sahih al-Bukhari, Muhammad made a similar statement about a (presumably young) slave that was in his midst:
Sahih al-Bukhari 6167
Narrated Anas:
A bedouin came to the Prophet (ﷺ) and said, "O Allah's Messenger (ﷺ)! When will The Hour be established?" The Prophet (ﷺ) said, "Wailaka (Woe to you), What have you prepared for it?" The bedouin said, "I have not prepared anything for it, except that I love Allah and His Apostle."
The Prophet (ﷺ) said, "You will be with those whom you love." We (the companions of the Prophet (ﷺ) ) said, "And will we too be so? The Prophet (ﷺ) said, "Yes." So we became very glad on that day. In the meantime, a slave of Al-Mughira passed by, and he was of the same age as I was. The Prophet (ﷺ) said. "If this (slave) should live long, he will not reach the geriatric old age, but the Hour will be established."
This binds the Last Hour to an even shorter time limit than it was with the little kid. This is obviously an end times prediction for all of the same reasons as the passage in Sahih Muslim.
Is that slave still alive today, 1,400 years later, miraculously preserved as a young man? What about the little kid? No, and no. Therefore, Muhammad was a false prophet.
Muhammad, at other times, said that in 100 years, no one would be alive:
Sahih al-Bukhari 564
Narrated `Abdullah:
"One night Allah's Messenger (ﷺ) led us in the `Isha' prayer and that is the one called Al-`Atma by the people. After the completion of the prayer, he faced us and said, "Do you know the importance of this night? Nobody present on the surface of the earth tonight will be living after one hundred years from this night."
This is also narrated in Sahih al-Bukhari 116. The Arabic in the passage actually says "not a single person on the surface of the earth will remain", but as I have covered over and over again in these articles on Islam, false, horrific, or embarrassing things are often obscured by lying Muslim translators, who have an agenda to deceive English speakers.
To a non-Muslim, this prophecy is clear. The world would end in less than or equal to 100 years from "this night". That's why he mentions "this night", and its significance. And, we see in other narrations, that at other times, Muhammad made a very similar statement when asked about "the Last Hour":
Sahih Muslim 2539
Abu Sa'id reported that when Allah's Apostle (ﷺ) came back from Tabuk they (his Companions) asked about the Last Hour. Thereupon Allah's Messenger (ﷺ) said:
There would be none amongst the created beings living on the earth (who would survive this century).
Sahih Muslim 2538a
Jabir b. 'Abdullah reported:
I heard Allah's Messenger (ﷺ) as saying this one month before his death: You asked me about the Last Hour whereas its knowledge is with Allah. I, however, take an oath and say that none upon the earth, the created beings, would survive at the end of one hundred years.
Even in spite of the obtuse, deceptive translations of these passages, the intended message is still clear. It's an end times prophecy, which sets a time bound of 100 years.
Since this is a failed prophecy, however, and Muslims need to reinterpret it, they assert that here, Muhammad was prophesying that no one that was presently alive on earth would live 100 years from that night.
This Muslim interpretation is absurd for a few reasons:
The only Muslim explanation is an embarrassingly irrational, ad-hoc justification for why Muhammad's prophecy failed. He set a date, and that date has long since passed. He was a false prophet.
The Hadith collections are filled with Muhammad's many statements on the end times, a good deal of which are ridiculous.
For instance, he taught that a sign of the Last Hour would be that something would happen to the buttocks of Pagan women who circumambulate a local idol:
Sahih al-Bukhari 7116
Narrated Abu Huraira:
Allah's Messenger (ﷺ) said, "The Hour will not be established till the buttocks of the women of the tribe of Daus move while going round Dhi-al-Khalasa." Dhi-al-Khalasa was the idol of the Daus tribe which they used to worship in the Pre Islamic Period of ignorance.
Whatever god this was is no longer worshipped anywhere, by anyone, and Dhi-al-Khalasa, which was a competing Kaaba (Sahih al-Bukhari 3823), has long since been destroyed by Muslims (Sahih al-Bukhari 3020, 4355-57, 6333), meaning this prophecy will never be fulfilled.
In addition, Muhammad taught that time would be constricted before the Last Hour:
Jami at-Tirmidhi 2332
Anas bin Malik narrated that the Allah's Messenger said:
"The hour shall not be established until time is constricted, and the year is like a month, a month is like the week, and the week is like the day, and the day is like the hour, and the hour is like the flare of the fire."
Taken plainly, this would mean that the earth spins faster, and that the speed of our rotation around the sun also increases. Since none of these things are ever going to happen (Genesis 8:22), Muhammad was a false prophet.
Moreover, he taught that before the Last Hour, Muslims would become so wealthy that they would run out of poor people to donate their Zakat to:
Sahih al-Bukhari 1412
Narrated Abu Huraira:
The Prophet (ﷺ) said, "The Hour (Day of Judgment) will not be established till your wealth increases so much so that one will be worried, for no one will accept his Zakat and the person to whom he will give it will reply, 'I am not in need of it.'"
The above is also narrated in Sahih al-Bukhari 1413, 2476, 7120. This is not even close to being a reality now, and never will be (John 12:8). Therefore, Muhammad was a false prophet.
He also taught that there would be a massive apostasy before the Last Hour, with many Muslims converting to idol worship:
Jami at-Tirmidhi 2219
Thawban narrated that the Messenger of Allah(s.a.w) said:
"The Hour shall not be established until tribes of my Ummah unite with the idolaters, and until they worship idols. And indeed there shall be thirty imposters in my Ummah, each of them claiming that he is a Prophet. And I am the last of the Prophets, there is no Prophet after me."
Many other narrations suggest this as well (Sahih al-Bukhari 1036, 7062-66, 7319), with some saying that the Last Hour will not come so long as Allah's name is pronounced in the earth (Sahih Muslim 148a-b, Jami at-Tirmidhi 2207), and will occur only after the Hajj is abandoned (Sahih al-Bukhari 1593).
To highlight another example:
Sahih Muslim 146
It is narrated on the authority of Ibn 'Umar ('Abdullah b. 'Umar) that the Messenger of Allah (ﷺ) observed:
Verily Islam started as something strange and it would again revert (to its old position) of being strange just as it started, and it would recede between the two mosques just as the serpent crawls back into its hole.
According to the above, Islam will diminish until its domain is only between the two mosques, just as it was during the time of Muhammad.
All of these indicate that Muhammad prophesied a total wipeout of Islam and Muslims (and even those who study Islam, and use the name of Allah), which is never going to happen, and also totally contradicts other prophecies he's given up to this point, and elsewhere (Sahih al-Bukhari 7312, 7459, Sahih Muslim 1925, etc.).
He also taught that before the Last Hour would come (and soon), the Euphrates would uncover a mountain of gold:
Sahih Muslim 2894a
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
The Last Hour would not come before the Euphrates uncovers a mountain of gold, for which people would fight. Ninety-nine out of each one hundred would die, but every man amongst them would say that perhaps he would be the one who would be saved (and thus possess this gold).
Sahih Muslim 2894d
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
The Euphrates would soon uncover a mountain of gold, but he who is present there should not take anything from that.
This is also narrated in Sahih al-Bukhari 7119, Sahih Muslim 2894c, 2895, and Sunan Abi Dawud 4313-14.
If Muslims believed their prophet, shouldn't they be relentlessly using radar to detect the mountain of gold under the Euphrates? If not to take some, at least to verify what Muhammad claimed? Of course not, because they know this is ridiculous.
In addition, he taught the bizarre "Gog and Magog" prophecy, in which an army restrained somewhere on earth by a large iron wall will invade the entire world (Surah 18:92-99, 21:95-97). This is covered in its own article here.
Finally, he taught that there will be a ratio of 50 women per man before the Last Hour:
Sahih al-Bukhari 6808
Narrated Anas:
I will narrate to you a narration which nobody will narrate to you after me. I heard that from the Prophet. I heard the Prophet (ﷺ) saying, "The Hour will not be established" or said: "From among the portents of the Hour is that the religious knowledge will betaken away (by the death of religious Scholars) and general ignorance (of religion) will appear; and the drinking of alcoholic drinks will be very common, and (open) illegal sexual intercourse will prevail, and men will decrease in number while women will increase so much so that, for fifty women there will only be one man to look after them."
The above is also narrated in Sahih al-Bukhari 81.
Instead of the above, what we see in the world is selective abortion against baby girls in the two most populous nations, India and China, so that their demographics are skewed to favor men. The ratio of women to men isn't even close to 50 to 1, even with allowance for overstatement. This is yet another ridiculous, impossible, false prophecy.
Muhammad taught his followers that the end was imminently approaching, and the 1,400 years between then and now testify that he was wrong. He also made a host of bizarre, impossible, and contradictory prophecies regarding the end of the world.
If you are a Muslim, you are trusting your Salvation to the same man who said all of this absolute nonsense.