Sahih al-Bukhari 1171

It is related that Mujhaid was heard to say, "Someone came to Ibn 'Umar in his house and told him that the Messenger of Allah, may Allah bless him and grant him peace, had entered the Ka'ba. He said, 'I went and found that the Messenger of Allah, may Allah bless him and grant him peace, had come out and I found Bilal standing at the door. I said, "Bilal! Did the Messenger of Allah, may Allah bless him and grant him peace, pray inside the Ka'ba?" He said, "Yes." I said, "Where?" He said, "Between these two pillars and then he came out and prayed two rak'ats in front of the Ka'ba."'" Abu Hurayra said, "The Prophet, may Allah bless him and grant him peace, ordered me to pray the two rak'ats of Duha." 'Itban said, "The Messenger of Allah, may Allah bless him and grant him peace, and Abu Bakr came to me in the morning after the day had begun and we formed rows behind him and he prayed two rak'ats."