Musannaf Ibn Abi Shayba 34:143

Ibn Numayr narrated to us, from Hajjaj, from Nafi’, from Ibn ‘Umar, who said: The Messenger of Allah (may Allah bless him and grant him peace) entered it, along with al-Fadl, Usama ibn Zayd, and Talha ibn ‘Uthman. Ibn ‘Umar said: So I entered, and the first person I met was Bilal. I said, "Where did the Prophet (may Allah bless him and grant him peace) pray?" He said, "Between these two pillars."