(139) باب كَمْ مَرَّةٍ يُسَلِّمُ الرَّجُلُ فِي الاِسْتِئْذَانِ
Abu Sa'id al-Khudri said:
I was sitting in one of the meeting of the Ansar. Abu Musa came terrified. We asked him; what makes you terrified? He replied: 'Umar sent for me; so I went to him and asked his permission three times, but he did not permit me (to enter), so I came back. He asked; what has prevented you from coming to me? I replied: I came and asked permission three times, but it was not granted to me (so I returned). The Messenger of Allah (May peace be upon him) has said: When one of you asks permission three times and it is not granted to him, he should go away. He ('Umar') said; establish the proof of it. So Abu Sa'id said: the youngest of the people will accompany you. So Abu Sa'id got up with him and testified.
Reference: Sunan Abi Dawud 5180
In-book reference: Book 43, Hadith 408
English translation: Book 42, Hadith 5161