Sunan An-Nasa'i

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