The battle of Khaybar was a battle between Muhammad's forces and the Jewish tribe Banu Nadir in 628 A.D., four years before Muhammad died.
Sirat Rasul Allah ("The Life of the Prophet"), which is the earliest biography of Muhammad, written by Ibn Ishaq (704-767) and Ibn Hisham (died 833), contains a section on the aftermath of the battle, in which Muhammad behaves in a truly merciless, contemptible way:
Sirat Rasul Allah, Guillaume, pg. 515
Kinana b. al-Rabi, who had the custody of the treasure of Banu al-Nadir, was brought to the apostle who asked him about it. He denied that he knew where it was. A Jew was brought to the apostle and said that he had seen Kinana going round a certain ruin every morning early. When the apostle said to Kinana, "Do you know that if we find you have it I shall kill you?" he said Yes. The apostle gave orders that the ruin was to be excavated and some of the treasure was found.
When he asked him about the rest he refused to produce it, so the apostle gave orders to al-Zubayr b. al-`Awwam, "Torture him until you extract what he has," so he kindled a fire with flint and steel on his chest until he was nearly dead. Then the apostle delivered him to Muhammad b. Maslama and he struck off his head, in revenge for his brother Mahmud.
"The model for all humanity" - "God's final messenger" - "The greatest man to ever live" - had a man tortured by having a fire lit on his chest because the man wouldn't tell him where money was hidden, then turned him over to have his head cut off.
Ibn Ishaq's testimony of Kenana's torture is confirmed by another authoritative commentator, Ibn Kathir (1300-1373 A.D.), who writes:
Ibn Kathir - The Life of the Prophet Muhammad, Le Gassick, Vol. 3, pg. 270
They then concealed a leather bag containing money and jewels belonging to Huyayy b. Akhtub; he had carried it with him to Khaybar when Banu al-Nadir was expelled. The Messenger of God asked at this time, "What happened to the leather bag of Huyayy that he brought from al-Nadir?" He replied, "Various expenses and the warfare have exhausted it."
The Messenger of God responded, "Only a little time has passed and there was more money than that." The Messenger of God then pushed him over to al-Zubayr who tortured him. Before this, Huyayy had gone inside a ruin and he reported seeing Huyayy circling it. They then went and searched, ultimately finding the bag in the ruin.
What we've read above is not the miraculous moral behavior that we would expect the final prophet of God to have, but rather sounds like the actions of any old cruel warlord who valued money over mercy. Muhammad, being a military dictator first, "prophet" second, showed his true colors when money was on the line, and he had the upper hand.
Also important to mention when discussing this event is the fact that Kenana, the man who was tortured and killed, was the husband of Safiyya, who Muhammad later married, after also having killed her father and brother at Khaybar. The account of his consummation of that marriage is recorded in the History of Al-Tabari:
The History of Al-Tabari, Vol. 39, pg. 185
Safiyyah had been married to Sallam b. Mishkam al-Qurazi, who divorced her, whereupon she was married to Kinanah b. al-Rabi' b. Abi al-Huqayq al-Nadari. The latter was killed in the battle of Khaybar, leaving her a widow.
Ibn `Umar [al-Waqidi]-Kathir b. Zayd-al-Walid b. Rabah Abu Hurayrah: While the Prophet was lying with Safiyyah Abu Ayyub stayed the night at his door. When he saw the Prophet in the morning he said "God is the Greatest." He had a sword with him; he said to the Prophet "O Messenger of God, this young woman had just been married, and you killed her father, her brother and her husband, so I did not trust her [not to harm] you." The Prophet laughed and said "Good."
Above, we see that one of Muhammad's companions is worried that Safiyya was going to try to kill Muhammad during their wedding night, seeing that he had just killed her father, brother, and husband. Muhammad finds that funny.
It is also reported that Safiyya was 16 or 17 years old when the 60 year-old Muhammad married her. Another detail is that she was already betrothed to one of Muhammad's companions when he heard how beautiful she was, and so he bought her for seven slaves (Sunan ibn-Majah 2272). She was also divorced, prior to being married to Kenana, making her marriage with Muhammad adulterous according to Jesus Christ (Luke 16:18).
Despite Muhammad's victory over, and slaughter of, Banu Nadir, he would not leave Khaybar the same as he arrived.
It was at Khaybar that the "prophet" received a "revelation" that he was eating poisoned food - only after eating some of it first - leading to a painful illness that would last for years, and ultimately, kill him:
Sunan Abu-Dawud 4512
Narrated Abu Hurairah:
The Messenger of Allah (ﷺ) would accept a present, but would not accept alms (sadaqah). And Wahb bin Baqiyyah narrated to us, elsewhere, from Khalid, from Muhammad ibn Amr said on the authority of AbuSalamah, and he did not mention the name of Abu Hurairah: The Messenger of Allah (ﷺ) used to accept presents but not alms (sadaqah).
This version adds: So a Jewess presented him at Khaybar with a roasted sheep which she had poisoned. The Messenger of Allah (ﷺ) ate of it and the people also ate. He then said: Take away your hands (from the food), for it has informed me that it is poisoned. Bishr ibn al-Bara' ibn Ma'rur al-Ansari died.
So he (the Prophet) sent for the Jewess (and said to her): What motivated you to do the work you have done? She said: If you were a prophet, it would not harm you; but if you were a king, I should rid the people of you. The Messenger of Allah (ﷺ) then ordered regarding her and she was killed. He then said about the pain of which he died: I continued to feel pain from the morsel which I had eaten at Khaybar. This is the time when it has cut off my aorta.
Note the hilarious "I just a received a revelation", only after he already tasted it. Also note the astounding stupidity of accepting a dinner from a woman whose tribe and family you had just slaughtered.
Did Allah want Muhammad to be poisoned, and slowly die over the next few years in agony, so he waited until after Muhammad already ate some poison to warn him? Why didn't Allah warn Muhammad sooner? Did Allah want a Jewish woman to poison, and kill Muhammad, and one of his companions?
This poisoning event, and the fact that it damaged Muhammad's mouth, and that he felt constant pain from this poisoning until he died, is mentioned in many Hadith, for instance:
Sahih al-Bukhari 4428
Narrated Aisha:
The Prophet in his ailment in which he died, used to say, O Aisha! I still feel the pain caused by the food I ate at Khaibar, and at this time, I feel as if my aorta is being cut from that poison.
Also see Sahih al-Bukhari 2617, 3169, 4249, 5777, and Sunan abu-Dawud 4508-4514 for other narrations of this poisoning event, and its effects.
In this instance, we have an example of a false prophet "reaping what he sowed" (Galatians 6:7). He sowed lighting a man on fire to get his treasure, and reaped an agonizing, fatal illness at the hand of a woman whose tribe he just conquered.
Also, just for fun, note that Muhammad could have been immune from the poison, had he followed his own prescription from elsewhere in the Sunnah, as we read:
Sahih al-Bukhari 5445
Narrated Sa`d:
Allah's Messenger (ﷺ) said, "He who eats seven 'Ajwa dates every morning, will not be affected by poison or magic on the day he eats them."
This is also narrated in Sahih al-Bukhari 5768, 5769, 5779, Sahih Muslim 2047a-b, and Sunan abu-Dawud 3876.
Muhammad was ostensibly too busy trying to violently subjugate the entire planet to take his dates the morning that he was poisoned.
Very interestingly, you'll note that twice above, Muhammad said that he felt that "his aorta" was being cut off. This is interesting, because that's precisely what he said Allah would do to him if he was a false prophet:
Surah 69:44-46
44 If [the Prophet] had attributed some fabrication to Us,
45 We would certainly have seized his right hand,
46 Then severed his aorta,
Of course, even according to Islam's own sources, Muhammad recited revelations from Satan, and was therefore deserving of this treatment, but it's poetic justice that God allowed Muhammad to die in this precise manner, in light of what his own fake scripture said.
And, if you ever want to see a Muslim scramble, and make up far-fetched, impossible, nonsense excuses, then show them the above. They cannot escape the incredible fact that Muhammad, according to himself, died in the exact manner that he said he would die if he were a false prophet.
The events at Khaybar show in many ways that Muhammad was a false prophet. He was a warmonger who wasn't above torturing people for money. He married a teenage girl when he was 60 years old, even though he already had many other wives, and had just killed her family. He received a "revelation" slightly after tasting poisoned food that wasn't able to save him from a painful death, and a death in the exact, precise manner that he himself said he would die if he were a false prophet.