Riyad as-Salihin
Riyad as-Salihin 871
Seeking Permission to Enter (Someone's House) and Manners Relating to It
Arabic hadith text
وعن سهل بن سعد قال: قال رسول الله صلى الله عليه وسلم : "إنما جعل الاستئذان من أجل البصر" ((متفق عليه)).
Translation
Sahl bin Sa'd (May Allah be pleased with him) reported
The Messenger of Allah (ﷺ) said, "Seeking permission to enter (somebody's house) has been prescribed in order to restrain the eyes (from looking at something we are not supposed to look at)."[Al-Bukhari and Muslim].