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.
حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُلَيْمَانُ بْنُ بِلاَلٍ، عَنْ يَحْيَى، عَنْ عُبَيْدِ بْنِ حُنَيْنٍ، سَمِعَ ابْنَ عَبَّاسٍ، عَنْ عُمَرَ ـ رضى الله عنهم ـ قَالَ جِئْتُ فَإِذَا رَسُولُ اللَّهِ صلى الله عليه وسلم فِي مَشْرُبَةٍ لَهُ، وَغُلاَمٌ لِرَسُولِ اللَّهِ صلى الله عليه وسلم أَسْوَدُ عَلَى رَأْسِ الدَّرَجَةِ فَقُلْتُ قُلْ هَذَا عُمَرُ بْنُ الْخَطَّابِ فَأَذِنَ لِي.
Bukhari
Accepting Information Given by a Truthful Person • Hadith 17