(3) بَابُ قَوْلِ اللَّهِ تَعَالَى: {لاَ تَدْخُلُوا بُيُوتَ النَّبِيِّ إِلاَّ أَنْ يُؤْذَنَ لَكُمْ}
Narrated `Umar:
I came and behold, Allah's Messenger (ﷺ) was staying on a Mashroba (attic room) and a black slave of Allah's Messenger (ﷺ) was at the top if its stairs. I said to him, "(Tell the Prophet) that here is `Umar bin Al- Khattab (asking for permission to enter)." Then he admitted me.
Reference: Sahih al-Bukhari 7263
In-book reference: Book 95, Hadith 17
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 9, Book 91, Hadith 368