Mishkat al-Masabih
Mishkat al-Masabih 3515
وَعَن سهل بنِ سعد: أَنَّ رَجُلًا اطَّلَعَ فِي جُحْرٍ فِي بَابِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَمَعَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مِدْرًى يَحُكُّ بِهِ رَأْسَهُ فَقَالَ: «لَوْ أَعْلَمُ أَنَّكَ تنظُرُني لطَعَنْتُ بهِ فِي عَيْنَيْكَ إِنَّمَا جُعِلَ الِاسْتِئْذَانُ مِنْ أَجْلِ الْبَصَرِ»
Sahl ibn Sa'd reported: A man looked through a hole in the door of the Messenger of God, while the Messenger of God had a metal scratcher with which he was scratching his head. He said: ‘Had I known you were looking at me, I would have poked it into your eyes. Permission to enter was prescribed only because of sight.’
Translation notes
The English witness adds Bukhari and Muslim as attribution; the Arabic passage supplied contains no source attribution.