Silsilat al-Ahadith al-Sahihah

It is narrated from Abu Sa'id and others, they say: Sayyiduna Abu Sa'id (may Allah be pleased with him) said: I was sitting in a gathering of the Ansar when suddenly Sayyiduna Abu Musa (may Allah be pleased with him), who was frightened and anxious, arrived there and said: I sought permission to go to Sayyiduna 'Umar (may Allah be pleased with him) three times, but I was not granted permission, so I turned back. Sayyiduna 'Umar (may Allah be pleased with him) asked me: What stopped you? I said: I sought permission three times, but I was not granted permission, so I was about to return, because the Messenger of Allah (peace and blessings be upon him) said: "When any man seeks permission (from someone) three times and he is not granted permission, then he should return." Sayyiduna 'Umar (may Allah be pleased with him) said: By Allah! You must present a witness for this hadith, (otherwise). Now you tell me, has anyone heard this hadith from the Prophet (peace and blessings be upon him)? Sayyiduna Ubayy ibn Ka'b (may Allah be pleased with him) said: By Allah! From this gathering, the one who is the youngest will stand with you. I (Abu Sa'id) was the youngest. I went with them and informed Sayyiduna 'Umar (may Allah be pleased with him) that I too had heard this hadith from the Prophet (peace and blessings be upon him).