Narrated 'Umar:

I came and behold, Allah's Apostle was staying on a Mashroba (attic room) and a black slave of Allah's Apostle 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 ﷺ فِي مَشْرُبَةٍ لَهُ، وَغُلاَمٌ لِرَسُولِ اللَّهِ ﷺ أَسْوَدُ عَلَى رَأْسِ الدَّرَجَةِ فَقُلْتُ قُلْ هَذَا عُمَرُ بْنُ الْخَطَّابِ فَأَذِنَ لِي.