Musnad Ahmad 1034:68

Husayn ibn Muhammad narrated to us, Isra'il narrated to us, from Abu Ishaq, from 'Abd al-Rahman ibn Yazid, who said: We came to Hudhayfah and said: "Direct us to the person who is closest to the Messenger of Allah, may Allah bless him and grant him peace, in guidance, manner, and conduct, so that we may take from him and listen to him." He said: "The person who was closest to the Messenger of Allah, may Allah bless him and grant him peace, in guidance, manner, and conduct was Ibn Umm 'Abd," until he disappeared from me into his house. And the preserved ones among the companions of Muhammad, may Allah bless him and grant him peace, certainly knew that Ibn Umm 'Abd was among those closest to Allah in proximity.