Mujahid said that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: "The Messenger of Allah (peace and blessings be upon him) entered the Ka'bah, and Bilal (may Allah be pleased with him) stood at the door." Ibn Umar (may Allah be pleased with them both) said: I asked Bilal (may Allah be pleased with him) whether the Messenger of Allah (peace and blessings be upon him) prayed. He said: Yes, "two rak'ahs in the middle of the House."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1027