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."
Sahih al-Bukhari Book 34, Hadith 15
The Messenger of Allah (ﷺ) used to say: “O Allah, I seek refuge in You from a heart that does not humble itself, and from a supplication that is not heard, and from a soul that is never satisfied, and from knowledge that does not benefit, I seek refuge in You from these four (Allāhumma innī a`ūdhu bika min qalbin lā yakhsha`u, wa min du`ā’in lā yusma`u, wa min nafsin lā tashba`u, wa min `ilmin lā yanfa`u, a`ūdhu bika min hā’ula’il-arba`).”
Jami` at-Tirmidhi Book 48, Hadith 113
"Aflah, the brother of Abu Al-Qu'ais, came and asked permission to enter, and I said: 'I will not let him in until I seek the permission of the Prophet of Allah.' When the Prophet of Allah came, I said to him: 'Aflah, the brother of Abu Al-Qu'ais, came and asked permission to enter, but I refused to let him in.' He said: 'Let him in, for he is your paternal uncle.' I said: 'The wife of Abu Al-Qu'ais breast-fed me; the man did not breast-feed me.' He said: 'Let him in, for he is your paternal uncle.'"
Sunan an-Nasa'i Book 26, Hadith 123