Musnad Ahmad 1290:1

Abu Kamil narrated to us, Ibrahim bin Sa’d narrated to us, Ibn Shihab narrated to us, and Ya’qub narrated to us, from my father, from Ibn Shihab, from Kharijah bin Zayd bin Thabit, from Umm al-Ala’—and she was a woman from their women—Ya’qub said: He informed him—that she pledged allegiance to the Messenger of Allah, may Allah bless him and grant him peace. She was allotted Uthman bin Maz’un for housing—Ya’qub said: It was drawn for them in the housing—when the Ansar drew lots for the housing of the Muhajirun. Umm al-Ala’ said: Uthman bin Maz’un fell ill with us, so we nursed him until, when he passed away, we wrapped him in his garments. The Messenger of Allah, may Allah bless him and grant him peace, entered upon us, and I said: "May the mercy of Allah be upon you, Abu al-Sa’ib. My testimony for you is that Allah has honored you." The Messenger of Allah, may Allah bless him and grant him peace, said: "And what makes you know that Allah has honored him?" She said: I said: "I do not know, may my father and mother be sacrificed for you." The Messenger of Allah, may Allah bless him and grant him peace, said: "As for him, certainty has come to him from his Lord, and I truly hope for good for him. By Allah, I do not know—and I am the Messenger of Allah—what will be done with me." Ya’qub said: "with him." She said: I said: "By Allah, I will never declare anyone pure after him ever." That saddened me, so I slept and I was shown a spring flowing for Uthman. I came to the Messenger of Allah, may Allah bless him and grant him peace, and informed him of that. The Messenger of Allah, may Allah bless him and grant him peace, said: "That is his deed."