Musannaf Ibn Abi Shayba 3:5910

'Affan narrated to us, he said: Aban ibn Yazid narrated to us, he said: Yahya ibn Abi Kathir narrated to us, from Abu Salamah ibn 'Abd al-Rahman, from Jabir ibn 'Abd Allah, he said: We approached with the Messenger of Allah, may Allah bless him and grant him peace, until when we were at Dhat al-Riqa', the call to prayer was made. He prayed two rak'ahs with one group, then they stepped back, and he prayed two rak'ahs with the other group. He said: So there were four rak'ahs for the Messenger of Allah, may Allah bless him and grant him peace, and two rak'ahs for the people.