An-Núr 24:29 ليس عليكم جناح ان تدخلوا بيوتا غير مسكونة فيها متاع لكم والله يعلم ما تبدون وما تكتمون ٢٩

Seeking Permission and the Etiquette of entering Houses

This is the Islamic etiquette. Allah taught these manners (of seeking permission) to His believing servants and commanded them not to enter houses other than their own until they had asked permission, i.e., to ask for permission before entering