Al-Adab Al-Mufrad, Book 43, Hadith 40 (In-Book) ⓘ
Muslim ibn Nadhir said, "A man asked permission to enter from Hudhayfa. He looked in and said, 'May I come in?' Hudhayfa replied, 'As for you eye, it has already entered. As for your bottom, it has not entered.'"
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، قَالَ: أَخْبَرَنَا سُفْيَانُ، عَنْ أَبِي إِسْحَاقَ، عَنْ مُسْلِمِ بْنِ نَذِيرٍ قَالَ: اسْتَأْذَنَ رَجُلٌ عَلَى حُذَيْفَةَ فَاطَّلَعَ وَقَالَ: أَدْخُلُ؟ قَالَ حُذَيْفَةُ: أَمَّا عَيْنُكَ فَقَدْ دَخَلَتْ، وَأَمَّا اسْتُكَ فَلَمْ تَدْخُلْ.
also referenced under: Hadith 1090 (Reference) & Book 43, Hadith 1090 (English)