Musnad Ahmad 3:97

Abdullah narrated to us, Al-Hakam ibn Musa Abu Salih narrated to me, Sa’id ibn Maslamah narrated to us, from Isma’il ibn Umayyah, from Musa ibn ‘Imran ibn Manah, from Aban ibn ‘Uthman: That he saw a funeral procession approaching, and when he saw it, he stood up. He said: "I saw ‘Uthman doing that, and he informed me that he saw the Prophet, may Allah bless him and grant him peace, doing it."