Musnad Ahmad 1034:110

'Affan narrated to us, Shu'bah narrated to us, he said: Abu Ishaq informed me, from 'Abd al-Rahman ibn Yazid, who said: We said to Hudhayfah: "Inform us of a man who is closest in manner and guidance 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 the wall of his house conceals him—than the son of Umm 'Abd." And we did not hear this from 'Abd al-Rahman ibn Yazid: "The preserved ones among the companions of Muhammad, may Allah bless him and grant him peace, certainly knew that the son of Umm 'Abd was among those closest to Allah in means."