Chapter 16: The Book of Pilgrimage
Abdullah b. Umar reported that he reached the Ka' ba and Allah' s Apostle (ﷺ) 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 (ﷺ) came out, and I went upstairs and entered the House and said: Where did Allah' s Apostle (ﷺ) observe prayer? They said: At this very place. I, however, forgot to ask them about the (number of) rak' ahs that he observed.
Sahih Muslim 1329e