Musnad Ahmad 941:13

'Abd al-Razzaq narrated to us, Ibn Jurayj informed us, he said: I said to 'Ata': Did you hear Ibn 'Abbas? And he mentioned a story, but I heard him say: Usama ibn Zayd informed me: That when the Prophet, peace and blessings of Allah be upon him, entered the House (the Ka'bah), he supplicated in all of its corners, and he did not pray in it until he exited. When he exited, he performed two rak'ahs facing the Ka'bah and said: "This is the Qiblah."