Mustadrak al-Hakim — Hadith 4594M

It is narrated from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) that he said on the pulpit: I saw in a dream as though a rooster pecked me three pecks (or he said: pecked me three times), so I said: "This is an a'jami (a non-Arab)." And I have entrusted this matter of the caliphate after me to these six men with whom the Messenger of Allah (peace and blessings be upon him) was pleased at the time of his death: Uthman, Ali, Talhah, al-Zubayr, Abd al-Rahman and Sa'd (may Allah be pleased with them).
This hadith has a sahih chain, but the two Shaykhs did not record it.
An account of the martyrdom of the Commander of the Faithful, Sayyiduna Uthman bin Affan (may Allah be pleased with him). The first thing of which a scholar may not be ignorant is knowing the cause of what happened to him: namely, the affair of Abdullah bin Sa'd bin Abi Sarh, who was the maternal cousin of Sayyiduna Uthman, and the affair of al-Walid bin Uqbah bin Abi Mu'ayt, who was his brother through his mother. As for Abdullah bin Sa'd bin Abi Sarh, the authentic reports state that he was a scribe of the Messenger of Allah (peace and blessings be upon him); then his breaches of trust in the writing became apparent, so the Messenger of Allah (peace and blessings be upon him) dismissed him, whereupon he apostatised and went off to Makkah. The Messenger of Allah (peace and blessings be upon him) had declared his blood lawful on the day of the Conquest of Makkah, but he was not killed until Sayyiduna Uthman (may Allah be pleased with him) brought him (after he had returned to Islam), so the Messenger of Allah (peace and blessings be upon him) granted him safety and spared his blood.