Musnad Ahmad 27:17

Hashim narrated to us, [and] more than one [person] informed us, and Ibn ‘Awn from Nafi‘, from Ibn ‘Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) entered the House [the Kaaba], and with him were al-Fadl ibn ‘Abbas, Usamah ibn Zayd, ‘Uthman ibn Talhah, and Bilal. He commanded Bilal, so he closed the door upon them. He remained in it for as long as Allah willed, then he came out. Ibn ‘Umar said: The first person I met among them was Bilal, so I said: "Where did the Messenger of Allah (peace and blessings of Allah be upon him) pray?" He said: "Right here, between the two pillars."