Narrated Abu Sa`id Al-Khudri: While I was present in one of the gatherings of the Ansar, Abu Musa came as if he was scared, and said, "I asked permission to enter upon `Umar three times, but I was not given the permission, so I returned." (When `Umar came to know about it) he said to Abu Musa, "Why did you not enter?'. Abu Musa replied, "I asked permission three times, and I was not given it, so I returned, for Allah's Apostle said, "If anyone of you asks the permission to enter thrice, and the permission is not given, then he should return.' " `Umar said, "By Allah! We will ask Abu Musa to bring witnesses for it." (Abu Musa went to a gathering of the Ansar and said). "Did anyone of you hear this from the Prophet ?" Ubai bin Ka`b said, "By Allah, none will go with you but the youngest of the people (as a witness)." (Abu Sa`id) was the youngest of them, so I went with Abu Musa and informed `Umar that the Prophet had said so. (See Hadith No. 277, Vol. 3)

Narrated 'Ubaid bin `Umair: Abu Musa asked `Umar to admit him but he was not admitted as `Umar was busy, so Abu Musa went back. When `Umar finished his job he said, "Didn't I hear the voice of `Abdullah bin Qais? Let him come in." `Umar was told that he had left. So, he sent for him and on his arrival, he (Abu Musa) said, "We were ordered to do so (i.e. to leave if not admitted after asking permission thrice). `Umar told him, "Bring witness in proof of your statement." Abu Musa went to the Ansar's meeting places and asked them. They said, "None amongst us will give this witness except the youngest of us, Abu Sa`id Al-Khudri. Abu Musa then took Abu Sa`id Al-Khudri (to `Umar) and `Umar said, surprisingly, "Has this order of Allah's Apostle been hidden from me?" (Then he added), "I used to be busy trading in markets."