Jami` at-Tirmidhi 3807

Narrated 'Abdur-Rahman bin Yazid:"We came to Hudhaifah and said: 'Inform us of the closest to the Messenger of Allah (ﷺ) in guidance and conduct, so that we may take from him and hear from him.' He said: 'The closest of the people in guidance, conduct, and character used to be 'Abdullah bin Mas'ud, until he would hide from us in his house. And the guarded ones (guarded by Allah from straying in word and deed) from the Companions of Muhammad (ﷺ) know that Ibn Umm 'Abd (a nickname for 'Abdullah bin Mas'ud) is from among the most intimately close to Allah of them