From Sahih Bukhari (Hadith 7018):
Narrated Kharija bin Zaid bin Thabit:Um Al-`Ala an Ansari woman who had given the Pledge of allegiance to Allah's Messenger (ﷺ) said, "`Uthman bin Maz'un came in our share when the Ansars drew lots to distribute the emigrants (to dwell) among themselves, He became sick and we looked after (nursed) him till he died. Then we shrouded him in his clothes. Allah's Messenger (ﷺ) came to us, I (addressing the dead body) said, "May Allah's Mercy be on you, O Aba As-Sa'ib! I testify that Allah has honored you." The Prophet (ﷺ) said, 'How do you know that?' I replied, 'I do not know, by Allah.' He said, 'As for him, death has come to him and I wish him all good from Allah. By Allah, though I am Allah's Messenger (ﷺ), I neither know what will happen to me, nor to you.'" Um Al-`Ala said, "By Allah, I will never attest the righteousness of anybody after that." She added, "Later I saw in a dream, a flowing spring for `Uthman. So I went to Allah's Messenger (ﷺ) and mentioned that to him. He said, 'That is (the symbol of) his good deeds (the reward for) which is going on for him
Reference: Bukhari 7018