Sahih al-Bukhari 5924
Sahih al-Bukhari · Book 77: Dress · Combing one's hair
Narrated Sa`d:
حَدَّثَنَا آدَمُ بْنُ أَبِي إِيَاسٍ ، حَدَّثَنَا ابْنُ أَبِي ذِئْبٍ ، عَنِ الزُّهْرِيِّ ، عَنْ سَهْلِ بْنِ سَعْدٍ ، أَنَّ رَجُلاً، اطَّلَعَ مِنْ جُحْرٍ فِي دَارِ النَّبِيِّ صلى الله عليه وسلم وَالنَّبِيُّ صلى الله عليه وسلم يَحُكُّ رَأْسَهُ بِالْمِدْرَى فَقَالَ " لَوْ عَلِمْتُ أَنَّكَ تَنْظُرُ لَطَعَنْتُ بِهَا فِي عَيْنِكَ، إِنَّمَا جُعِلَ الإِذْنُ مِنْ قِبَلِ الأَبْصَارِ " .
A man peeped into the house of the Prophet (ﷺ) through a hole while the Prophet (ﷺ) was scratching his head with a Midrai (a certain kind of comb). On that the Prophet (ﷺ) said (to him), "If I had known you had been looking, then I would have pierced your eye with that instrument, because the asking of permission has been ordained so that one would not see things unlawfully."