Sahih Bukhari, Chapter: Prayers (Salat)

Ibn 'Umar said, "The Prophet arrived at Mecca and sent for 'Uthman bin Talha. He opened the gate of the Ka'ba and the Prophet, Bilal, Usama bin Zaid and 'Uthman bin Talha entered the Ka'ba and then they closed its door (from inside). They stayed there for an hour, and then came out." Ibn 'Umar added, "I quickly went to Bilal and asked him (whether the Prophet had prayed). Bilal replied, 'He prayed in it.' I asked, 'Where?' He replied, 'Between the two pillars.' "Ibn 'Umar added, "I forgot to ask how many Rakat he (the Prophet) had prayed in the Ka'ba."