Sahih Muslim , Book 7, Hadith 3072 (USC-MSA) ⓘ

Abdullah b. Umar reported that he reached the Ka'ba and Allah's Apostle had entered therein, and Bilal and Usama too. 'Uthman b. Talha closed the door to them, and they stayed there for a considerable time, and then the door was opend and Allah's Apostle came out, and I went upstairs and entered the House and said: Where did Allah's Apostle observe prayer? They said: At this very place. I, however, forgot to ask them about the (number of) rak'ahs that he observed.

وَحَدَّثَنِي حُمَيْدُ بْنُ مَسْعَدَةَ، حَدَّثَنَا خَالِدٌ، - يَعْنِي ابْنَ الْحَارِثِ - حَدَّثَنَا عَبْدُ اللَّهِ، بْنُ عَوْنٍ عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ انْتَهَى إِلَى الْكَعْبَةِ وَقَدْ دَخَلَهَا النَّبِيُّ صلى الله عليه وسلم وَبِلاَلٌ وَأُسَامَةُ وَأَجَافَ عَلَيْهِمْ عُثْمَانُ بْنُ طَلْحَةَ الْبَابَ قَالَ فَمَكَثُوا فِيهِ مَلِيًّا ثُمَّ فُتِحَ الْبَابُ فَخَرَجَ النَّبِيُّ صلى الله عليه وسلم وَرَقِيتُ الدَّرَجَةَ فَدَخَلْتُ الْبَيْتَ فَقُلْتُ أَيْنَ صَلَّى النَّبِيُّ صلى الله عليه وسلم قَالُوا هَا هُنَا ‏.‏ قَالَ وَنَسِيتُ أَنْ أَسْأَلَهُمْ كَمْ صَلَّى.