Virtues of the Prayer Hall (Sutra of the Musalla)

Bukhari :: Book 1 :: Volume 9 :: Hadith 483

Narrated Ibn 'Umar:

The Prophet entered the Ka'ba along with Usama bin Zaid, 'Uthman bin Talha and Bilal and remained there for a long time. When they came out, I was the first man to enter the Ka'ba. I asked Bilal "Where did the Prophet pray?" Bilal replied, "Between the two front Pillars."