Sahih al-Bukhari Hadith 4400

Narrated (Abdullah) bin `Umar: The Prophet (ﷺ) arrived (at Mecca) in the year of the Conquest (of Mecca) while Usama was riding behind him on (his she-camel)'. Al-Qaswa.' Bilal and `Uthman bin Talha were accompanying him. When he made his she-camel kneel down near the Ka`ba, he said to `Uthman, "Get us the key (of the Ka`ba). He brought the key to him and opened the gate (of the Ka`ba), for him. The Prophet, Usama, Bilal and `Uthman (bin Talha) entered the Ka`ba and then closed the gate behind them (from inside). The Prophet (ﷺ) stayed there for a long period and then came out. The people rushed to get in, but I went in before them and found Bilal standing behind the gate, and I said to him, "Where did the Prophet (ﷺ) pray?" He said, "He prayed between those two front pillars." The Ka`ba was built on six pillars, arranged in two rows, and he prayed between the two pillars of the front row leaving the gate of the Ka`ba at his back and facing (in prayer) the wall which faces one when one enters the Ka`ba. Between him and that wall (was the distance of about three cubits). But I forgot to ask Bilal about the number of rak`at the Prophet (ﷺ) had prayed. There was a red piece of marble at the place where he (i.e. the Prophet) had offered the prayer.