Musnad Ahmad 612:9

'Abd al-Rahman ibn Mahdi narrated to us, Mu'awiyah narrated to us, from Sulaym ibn 'Amir, from Jubayr ibn Nufayr, who said: We were encamped with Mu'awiyah after the killing of 'Uthman. Then Ka'b ibn Murrah al-Bahzi stood up and said: "Were it not for something I heard from the Messenger of Allah (peace and blessings of Allah be upon him), I would not have stood in this position." When he heard the mention of the Messenger of Allah (peace and blessings of Allah be upon him), he made the people sit down. He said: "While we were with the Messenger of Allah (peace and blessings of Allah be upon him), 'Uthman ibn 'Affan passed by, having groomed his hair. The Messenger of Allah (peace and blessings of Allah be upon him) said: 'A tribulation will surely emerge from beneath the feet of this man, or from between his legs. He and those who follow him will be upon guidance on that day.'" He said: Then Ibn Hawalah al-Azdi stood up from by the pulpit and said: "Are you the one who is the subject of this?" He said: "Yes." He said: "By Allah, I was present at that gathering, and had I known that I would have a witness in the army, I would have been the first to speak of it."