Riyad as-Saliheen 870
Abu Musa Al-Ash'ari (May Allah be pleased with him) reported:
The Messenger of Allah ﷺ 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 ﷺ : “ الاستئذان ثلاث، فإن أذن لك وإلا فارجع" ((متفق عليه))
Classification
Sahih (Authentic)
References
Riyad as-Saliheen 870
Riyad as-Saliheen Book of Greetings, Hadith 26