Riyad as-Salihin, Book 6, Hadith 870 (In-Book) ⓘ
Abu Musa Al-Ash'ari (May Allah be pleased with him) reported: The Messenger of Allah said, "Permission is to be sought thrice. If it is accorded, you may enter; otherwise, go back."[Al- Bukhari and Muslim].
وعن أبي موسي الأشعري رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : “ الاستئذان ثلاث، فإن أذن لك وإلا فارجع" ((متفق عليه))