Zayd bin Wahb (may Allah have mercy on him) says: I was sitting with Sayyiduna Hudhayfah and Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with them both) when one of them said to the other: Have you heard the Messenger of Allah (peace and blessings be upon him) say such-and-such a hadith? He said: No. The other said to him: Then did you hear it yourself? He said: No. He said: The man of this house (Abdullah bin Mas'ud) claims that he heard it. Sayyiduna Abu Musa (may Allah be pleased with him) said: "If so, he used to enter upon the Prophet (peace and blessings be upon him) even when we were kept behind the curtain, and he used to be present even when we were absent." Sulayman al-A'mash says: "By this he meant Abdullah bin Mas'ud."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8460