صحيح البخاري

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 Messenger (ﷺ) been hidden from me?" (Then he added), "I used to be busy trading in markets."