Sunan Abi Dawud 5180
General Behavior (Kitab Al-Adab)
How many times should one say salam when seeking permission to enter
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 (ﷺ) 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.