Musnad Ahmad 27:617

He said: I found in my father’s book: Muhammad ibn Ja’far and Hajjaj narrated to us. Muhammad said: Shu’bah narrated to us. And Hajjaj said: Shu’bah narrated to me, from Simak al-Hanafi, who said: I heard Ibn Umar saying: "Indeed, the Messenger of Allah (peace and blessings of Allah be upon him) prayed inside the House (the Kaaba)." And you will come upon those who will forbid you from it.