رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 870
The Book of Greetings
Seeking Permission to Enter (Someone's House) and Manners Relating to It
وَعَنْ أَبِي موسي اَلْأَشْعَرِيِّ رَضِيَ اللَّه عَنْهُ قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ : “ الاِسْتِئْذَانُ ثَلاَثٌ، فَإِنْ أُذِنَ لَكَ وَإِلاَّ فَارْجِعْ" ((مُتَّفَقٌ عَلَيْهِ))
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 permission is granted, you may enter; otherwise, go back." [Al- Bukhari and Muslim].
Riyad as-Salihin, 870