Sahih al-Bukhari 40

Amr ibn Khalid narrated to us. He said: Zuhayr narrated to us. He said: Abu Ishaq narrated to us, from al-Bara': When the Prophet (peace and blessings be upon him) first came to Medina, he stayed with his ancestors—or, he said, his maternal uncles—from among the Ansar. He prayed toward Bayt al-Maqdis for sixteen or seventeen months. He liked for his direction of prayer to be toward the House. The first prayer he prayed toward the House was the afternoon prayer, and some people prayed with him. One of those who prayed with him went out and passed by people in a mosque while they were bowing. He said: ‘I call Allah to witness that I prayed with the Messenger of Allah (peace and blessings be upon him) facing Mecca.’ They turned, as they were, to face the House. The Jews and the People of the Book had been pleased that he prayed toward Bayt al-Maqdis, but when he turned his face toward the House, they disapproved of that.

Zuhayr said: Abu Ishaq narrated to us from al-Bara' in this report that, before the direction of prayer was changed, men had died facing the former direction and had been killed; we did not know what to say about them. Then Allah Most High revealed: ‘Allah would never let your faith go to waste.’