Musnad Ahmad 1034:172

Yahya narrated to us, from Shu'bah, Abu Ishaq narrated to us, from Abd al-Rahman ibn Yazid, who said: We said to Hudhayfah: "Inform us of a man who is closest in guidance, manner, and conduct to the Messenger of Allah, may Allah bless him and grant him peace, so that we may take from him." He said: "I do not know anyone who is closer in manner, guidance, and conduct to the Messenger of Allah, may Allah bless him and grant him peace—until he is hidden by the wall of his house—than the son of Umm 'Abd."