Musannaf Ibn Abi Shayba 3:995

Zayd ibn al-Hubab narrated to us, from Jamil ibn Ubayd al-Ta'i, from Thumamah, from his grandfather Anas ibn Malik, who said: The announcer of the Messenger of Allah (may Allah bless him and grant him peace) came and said: "Indeed, the Qibla has been turned toward the Sacred House." The Imam had already prayed two rak'ahs, so they turned around and prayed the remaining two rak'ahs toward the Ka'bah.