Musnad Ahmad 27:1494

Aswad ibn Amir narrated to us, Sinan ibn Harun narrated to us, from Kulayb ibn Wa'il, from Ibn Umar, who said: The Messenger of Allah, peace and blessings of Allah be upon him, mentioned a trial (fitnah). A man passed by and he said: "This veiled man will be killed in it on that day, oppressed." He said: So I looked, and behold, it was Uthman ibn Affan.