Sunan an-Nasa'i, Volume 3, Book 24, Hadith 2908 (DarusSalam) ⓘ

It was narrated from Abdullah bin Umar that: he came to the Kabah when the Prophet, Bilal and Usamah bin Zaid had enter it, and Uthman bin Talhah had shut the door. They stayed there for a while, then he opened the door and the Prophet came out. I (Ibn Umar) Climed the steps and entered the House and said: "Where did the Prophet pray?" They said: "Here." And I forgot to ask them how many (Rakahs) the Prophet had prayed inside the House.

أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا ابْنُ عَوْنٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ انْتَهَى إِلَى الْكَعْبَةِ وَقَدْ دَخَلَهَا النَّبِيُّ صلى الله عليه وسلم وَبِلاَلٌ وَأُسَامَةُ بْنُ زَيْدٍ وَأَجَافَ عَلَيْهِمْ عُثْمَانُ بْنُ طَلْحَةَ الْبَابَ فَمَكَثُوا فِيهَا مَلِيًّا ثُمَّ فَتَحَ الْبَابَ فَخَرَجَ النَّبِيُّ صلى الله عليه وسلم وَرَكِبْتُ الدَّرَجَةَ وَدَخَلْتُ الْبَيْتَ فَقُلْتُ أَيْنَ صَلَّى النَّبِيُّ صلى الله عليه وسلم قَالُوا هَا هُنَا ‏.‏ وَنَسِيتُ أَنْ أَسْأَلَهُمْ كَمْ صَلَّى النَّبِيُّ صلى الله عليه وسلم فِي الْبَيْتِ ‏.‏