Sahih Muslim | Book 7 | Hadith Number 3072

Narrated by Abdullah b. Umar
Abdullah b. Umar reported that he reached the Ka'ba and Allah's Apostle (may peace be upon him) 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 opened and Allah's Apostle (may peace be upon him) came out, and I went upstairs and entered the House and said: Where did Allah's Apostle (may peace be upon him) observe prayer? They said: At this very place. I, however, forgot to ask them about the (number of) rak'ahs that he observed.