Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
bukhari:7263ʿAbd al-ʿAzīz b. ʿAbdullāh > Sulaymān b. Bilāl > Yaḥyá > ʿUbayd b. Ḥunayn > Ibn ʿAbbās > ʿUmar

I came and behold, Messenger of Allah ﷺ was staying on a Mashroba (attic room) and a black slave of Messenger of Allah ﷺ was at the top if its stairs. I said to him, "(Tell the Prophet) that here is ʿUmar bin Al- Khattab (asking for permission to enter)." Then he admitted me.  

البخاري:٧٢٦٣حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ عَبْدِ اللَّهِ حَدَّثَنَا سُلَيْمَانُ بْنُ بِلاَلٍ عَنْ يَحْيَى عَنْ عُبَيْدِ بْنِ حُنَيْنٍ سَمِعَ ابْنَ عَبَّاسٍ عَنْ عُمَرَ ؓ 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