Zayd bin Wahb (may Allah have mercy on him) narrates: I was sitting with Hudhayfah (may Allah be pleased with him) when Abdullah bin Mas'ud and Abu Musa al-Ash'ari (may Allah be pleased with them both) passed by, and Hudhayfah (may Allah be pleased with him) said: "I bear witness that the better of you two, and the one who most resembles the Messenger of Allah (peace and blessings be upon him) in conduct and bearing, is Abdullah bin Mas'ud."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8459