The Book of Manners and Etiquette
Ṣaḥīḥ Muslim 5639
لَوْ أَعْلَمُ أَنَّكَ تَنْظُرُ طَعَنْتُ بِهِ فِي عَيْنِكَ إِنَّمَا جَعَلَ اللَّهُ الإِذْنَ مِنْ أَجْلِ الْبَصَرِ
law aʿlamu annaka tanẓuru ṭaʿantu bihi fī ʿaynika innamā jaʿala-Llāh al-idhna min ajli al-baṣari
Transliteration generated from the Arabic vowel marks
The full narration
Sahl b. Sa'd as-Sa'idi reported that a person peeped through the hole of the door of Allah's Messenger (ﷺ) and he had with him some pointed thing with which he had been adjusting (the hair of his head). Allah's Messenger (ﷺ) said to him:If I were to know that you had been peeping. I would have thrust it in your eyes. Allah has prescribed seeking permission because of protection against glance
Source
Ṣaḥīḥ Muslim · 5639
Ṣaḥīḥ