Sahih Bukhari Volume 1, Book 9, Hadith Number 483

Narated By 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.”