Narrated 'Um al-'Ala:
An Ansari woman who gave the pledge of allegiance to the Prophet that the Ansar drew lots concerning the dwelling of the Emigrants. 'Uthman bin Maz'un was decided to dwell with them (i.e. Um al-'Ala's family), 'Uthman fell ill and I nursed him till he died, and we covered him with his clothes. Then the Prophet came to us and I (addressing the dead body) said, "O Abu As-Sa'ib, may Allah's Mercy be on you! I bear witness that Allah has honored you." On that the Prophet said, "How do you know that Allah has honored him?" I replied, "I do not know. May my father and my mother be sacrificed for you, O Allah's Apostle! But who else is worthy of it (if not 'Uthman)?" He said, "As to him, by Allah, death has overtaken him, and I hope the best for him. By Allah, though I am the Apostle of Allah, yet I do not know what Allah will do to me," By Allah, I will never assert the piety of anyone after him. That made me sad, and when I slept I saw in a dream a flowing stream for 'Uthman bin Maz'un. I went to Allah's Apostle and told him of it. He remarked, "That symbolizes his (good) deeds."
Sahih al-Bukhari, Volume 5, Book 58, Number 266