Immediately preceding Muhammad's poisoning was the Battle of Khaybar (628-629 AD), in which Muhammad's forces fought against the Jewish tribe Banu Nadir. The result of the battle was a victory for the Muslims, and a surrender of Banu Nadir, which included an agreement to give 50% of their yearly harvest to the Muslims (Sahih al-Bukhari 2338, 4248, Sahih Muslim 1551a).
Additionally, Sirat Rasul Allah ("The Life of the Prophet"), which is the earliest biography of Muhammad, written by Ibn Ishaq (704-767 AD) and Ibn Hisham (died 833 AD), contains a section on the aftermath of the battle, which contains the following disturbing scene:
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.
Above, Muhammad is said to have told his companions to torture Kenana ibn al-Rabi from Banu Nadir, who knew where the tribe's treasure was hidden. His companions light a fire on his chest, and then he is delivered over to be beheaded. Muhammad's actions in this account seem exceptionally merciless, especially given that the directive to torture Kenana was given principally to recover money - "Torture him until you extract what he has".
Muhammad would also marry the widow of Kenana, Safiyya bint Huyayy, shortly after the battle, who he allegedly purchased for seven slaves from Dihyah al-Kalbi (Sunan Ibn Majah 2272).
After the Battle of Khaybar, a woman from the tribe of Banu Nadir named Zaynab bint Al-Harith offered Muhammad a dinner, which he accepted. However, she had poisoned the roasted sheep that she gave him, and though it did not kill him, it apparently did kill one of his companions:
Sunan Abi 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.
The above narration has Muhammad say that the sheep "informed" him that it was poisoned, after he had already eaten some of it, which is obviously illogical.
However, there are many narrations which, while lacking that detail, testify to the fact that Muhammad was indeed poisoned by a Jewish woman at Khaybar, and that he continued to feel the effects of the poison until he died:
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, Sahih Muslim 2190a-b, and Sunan Abi Dawud 4508-4514 for other narrations of this poisoning event, and its effects.
So, it can be stated with little controversy that Muhammad was successfully poisoned by a Jewish woman whose tribe he had conquered. This poisoning affected him up until the time of his death, years after the event, and probably contributed to it.
Also worth noting is that in both of the above narrations, as well as Sunan Abi Dawud 4513, Muhammad is said to have stated, "I feel as if my aorta is being cut from that poison", and "This is the time when it has cut off my aorta".
This is almost a word-for-word description of what he had said would happen to him, in the Quran, if he had fabricated revelations:
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,
There are many ways to die, and Muhammad's oddly-specific description of his aorta being severed is certainly odd, in light of the above verses.
The events at Khaybar should trouble Muslims. Muhammad is said to have ordered the torture of a man over a matter involving money. He unwisely accepted a meal from a woman whose tribe he had just violently conquered, and was successfully poisoned as a result. He then died oddly professing that his aorta was being severed, after that is what he revealed would happen to him if he had fabricated revelations from God.