Musnad Ahmad 3:59

Zakariya ibn Abi Zakariya narrated to us, Yahya ibn Sulaym narrated to us, Isma'il ibn Umayyah narrated to us, from 'Imran ibn Manah, who said: Aban ibn 'Uthman saw a funeral procession and stood up for it. He said: 'Uthman ibn 'Affan saw a funeral procession and stood up for it, then he narrated that the Messenger of Allah, peace and blessings of Allah be upon him, saw a funeral procession and stood up for it.