Sunan Abi Dawud 5181
General Behavior (Kitab Al-Adab)
How many times should one say salam when seeking permission to enter
Abu Musa said that he came to ‘Umar and asked permission three times saying : Abu Musa asks permission, al-Ash’ari ask permission, and ‘Abd Allah b. Qais asks permission, but it was not granted to him. So he went away and ‘umar sent for him saying: what did you return? He replied: The Messenger of Allah (ﷺ) said: When one of you asks permission three times and it is not granted to him, he should go away. He said: Establish the proof of it. He went, came back, and said; This is Ubayy. Ubayy said: ‘Umar, do not be an agony for the Companions of the Messenger of Allah (peace be upon him). ‘Umar said : I shall not be an agony for the Companions of the Messenger of Allah (ﷺ).