THE REASON FOR ASKING PERMISSION TO ENTER H 884 "Asking for permission has been prescribed in order to restrain the eyes." R 884 Bukhari and Muslim with a chain up to Sahl, the son of Sa'ad who related that the Prophet, praise and peace be upon him, said this.
871- وعن سهلِ بنِ سعدٍ رضي الله عنه ، قَالَ : قَالَ رسول الله صلى الله عليه وآله وسلم : "إنَّمَا جُعِلَ الاسْتِئذَانُ مِنْ أجْلِ البَصَرِ" متفقٌ عَلَيْهِ .