Musnad Ahmad 3:82

Bishr ibn Shu‘ayb narrated to us, my father narrated to me, from al-Zuhri, ‘Urwah ibn al-Zubayr narrated to me that ‘Ubayd Allah ibn ‘Adi ibn al-Khiyar informed him that ‘Uthman ibn ‘Affan said to him: "O son of my brother, did you reach the Messenger of Allah, may Allah bless him and grant him peace?" He said: I said to him: "No, but there reached me of his knowledge and certainty what reaches the virgin in her private quarters." He said: Then he testified, and then said: "As for what follows: Indeed, Allah, the Mighty and Majestic, sent Muhammad, may Allah bless him and grant him peace, with the truth. I was among those who responded to Allah and His Messenger, and I believed in that which Muhammad, may Allah bless him and grant him peace, was sent with. Then I performed the two migrations, as I have said, and I attained the kinship of the Messenger of Allah, may Allah bless him and grant him peace, and I pledged allegiance to the Messenger of Allah, may Allah bless him and grant him peace. By Allah, I did not disobey him, nor did I deceive him, until Allah, the Mighty and Majestic, took his soul."