Uthman's (may Allah be pleased with him) dream of the Prophet (peace and blessings be upon him) saying to him "Break your fast with us"

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that Sayyiduna Uthman bin Affan (may Allah be pleased with him) related in the morning, saying: "Last night I saw the Prophet (peace and blessings be upon him) in a dream, and he (peace and blessings be upon him) said to me: 'O Uthman! Break your fast with us today.'" So Sayyiduna Uthman (may Allah be pleased with him) began that day fasting, and on that very day he was martyred.
The chain of this hadith is sahih, but the two Shaykhs did not record it.

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both); he said: I was sitting with the Prophet (peace and blessings be upon him) when suddenly Sayyiduna Uthman bin Affan (may Allah be pleased with him) arrived. When he drew near to him (peace and blessings be upon him), he (peace and blessings be upon him) said: "O Uthman! You will be martyred while reciting Surah al-Baqarah, and a drop of your blood will fall upon this statement of Allah: 'So Allah will suffice you against them' [Surah al-Baqarah: 137]. The people of the East and the West will envy you, you will intercede for people as many as (the tribes of) Rabi'ah and Mudar, and on the Day of Resurrection you will be raised as the leader of everyone who was forsaken (in the world)."
Imam al-Hakim says: I have mentioned the musnad reports of this chapter in my book "Maqtal Uthman" (The Killing of Uthman), so I did not consider it appropriate to mention all of them here, since mentioning this much is sufficient. As for the claim made by the innovators that the Commander of the Faithful, Ali bin Abi Talib (may Allah be pleased with him), assisted in his killing, it is a lie and a slander; on the contrary, there are mass-transmitted (mutawatir) reports:

It is narrated from Qays bin Ubad; he said: I heard Sayyiduna Ali (may Allah be pleased with him) say on the day of the Battle of the Camel: "O Allah! I declare before You my innocence of the blood of Uthman. On the day Uthman was martyred, my mind was in a whirl and I did not even recognise myself. The people wanted to give me the pledge of allegiance, and I said: 'By Allah! I feel shy before Allah to accept the pledge of people who killed a man about whom the Messenger of Allah (peace and blessings be upon him) said: "Should I not feel shy before one before whom even the angels feel shy?"' And shyness before Allah also held me back from accepting the pledge while Uthman lay slain on the ground and had not yet even been buried. So they went away. Then when he had been buried, the people came to me again and demanded the pledge of allegiance, and only then was the burden on my heart lightened. Then I supplicated: 'Allahumma khudh minni li-Uthman hatta tarda' (O Allah, take retribution from me for Uthman's right until You are pleased)."

It is narrated from al-Hatibi Abd al-Rahman bin Muhammad, from his father, from his grandfather; he said: On the day of the Battle of the Camel, I went out to look at the bodies of the slain. He said: Sayyiduna Ali, Hasan bin Ali, Ammar bin Yasir, Muhammad bin Abi Bakr and Zayd bin Suhan (may Allah be pleased with them) were going around among the slain. Sayyiduna Hasan bin Ali (may Allah be pleased with them both) saw a slain man lying face down; he turned him onto his back, then cried out and said: "Inna lillahi wa inna ilayhi raji'un (We belong to Allah and to Him we return). By Allah! This is the prince of Quraysh." His father (Sayyiduna Ali (may Allah be pleased with him)) asked: "O my son! Who is he?" He said: "This is Muhammad bin Talhah bin Ubaydullah." Sayyiduna Ali (may Allah be pleased with him) said: "Inna lillahi wa inna ilayhi raji'un (We belong to Allah and to Him we return). By Allah! He was a most righteous young man." Then he sat down, deeply grieved and sorrowful. Sayyiduna Hasan (may Allah be pleased with him) said to him: "O my father! I used to try to stop you from this expedition, but the opinion of so-and-so and so-and-so prevailed over you." Sayyiduna Ali (may Allah be pleased with him) said: "O my son! So it was, and I wish that I had died twenty years before this event." Muhammad bin Hatib says: Then I stood up and said: "O Commander of the Faithful! We are going to Madinah, and people will ask us about Uthman (may Allah be pleased with him); what answer shall we give about him?" The narrator says: At this Ammar bin Yasir and Muhammad bin Abi Bakr (may Allah be pleased with them) spoke up and said certain things about Uthman (may Allah be pleased with him). Sayyiduna Ali (may Allah be pleased with him) said to them both: "O Ammar and O Muhammad! You both say that Uthman showed preference (to his relatives) and did not govern well; and by Allah! The punishment you gave him was also most evil, and soon you will be brought before a just Judge (Allah Almighty) who will judge between you." Then Sayyiduna Ali (may Allah be pleased with him) said: "O Muhammad bin Hatib! When you reach Madinah and are asked about Uthman, say: By Allah! He was among those who 'believed, then feared Allah and believed, then feared Allah and did good; and Allah loves those who do good' [Surah al-Ma'idah: 93], and upon Allah alone let the believers rely."

It is narrated from Amr bin Sufyan; he said: Sayyiduna Ali (may Allah be pleased with him) addressed us on the day of the Battle of the Camel and asked: "In which direction did the bulk of the people turn (during the battle)?" We said: "They lie slain around the camel (on which Sayyidah Aishah (may Allah be pleased with her) was mounted)." The narrator says: Then he (may Allah be pleased with him) said: "To proceed: The Messenger of Allah (peace and blessings be upon him) did not take from us any definite covenant regarding this leadership (the caliphate) in whose footsteps we could follow; rather, we saw it through our own insight. Sayyiduna Abu Bakr (may Allah be pleased with him) was made caliph, and he established the truth and remained steadfast; then Sayyiduna Umar (may Allah be pleased with him) was made caliph, and he too established the truth and remained steadfast; then circumstances changed and tribulations raised their heads."

It is narrated from al-Hakam; he said: Eighty Companions who had fought at Badr, and two hundred and fifty Companions who had given the pledge under the tree (the Pledge of Ridwan), were present with Sayyiduna Ali (may Allah be pleased with him) at (the Battle of) Siffin.

Abu Abdullah Muhammad bin Ya'qub informed us; al-Khadir bin Aban al-Hashimi narrated to us; Ali bin Qadim narrated to us; Abu Isra'il narrated to us from al-Hakam; he said: "They were present with Sayyiduna Ali (may Allah be pleased with him) at Siffin" (the complete text is the same as hadith number 4609).

It is narrated from Rib'i bin Hirash; he said: I went to Sayyiduna Hudhayfah (may Allah be pleased with him) in al-Mada'in in the days when people had set out (for strife and disorder) against Sayyiduna Uthman (may Allah be pleased with him). He asked: "O my son! What have your people done?" I said: "About which of their conditions are you asking?" He said: "Which of them has gone out (in rebellion) against this man (Uthman (may Allah be pleased with him))?" So I named to him a man who had gone out (towards Madinah), and he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever leaves the Jama'ah (the main body of the Muslims) and holds leadership (authority and command) in contempt will meet Allah in a state where he has no excuse or argument (in his defence) before Allah."

It is narrated from Maymun bin Mihran that Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) said: It would not please me at all to have raised my sword in the killing of Uthman, even if in exchange I were given this entire world and all that is in it.

Harun bin Antarah narrates from his father; he said: I saw Sayyiduna Ali (may Allah be pleased with him) at al-Khawarnaq. He was seated on a couch, and with him was sitting Aban bin Uthman (the son of Uthman (may Allah be pleased with him)). He (may Allah be pleased with him) said: I hope that I and your father (Uthman (may Allah be pleased with him)) will be among those about whom Allah, the Mighty and Majestic, has said: "And We shall remove whatever rancour is in their hearts; as brothers, on couches facing one another." [Surah al-Hijr: 47]