Abd al-Rahman bin al-Zajjaj said: I said to Shaybah bin Uthman (may Allah be pleased with him): O Abu Uthman! People claim that the Messenger of Allah (peace and blessings be upon him) entered the Ka'bah and did not pray in it? He said: They have lied. He (peace and blessings be upon him) prayed two rak'ahs between the two pillars, then pressed his stomach and his back against them.
Hadith Referenceالمعجم الكبير للطبراني / باب الشين / 7159