Musnad Abu Ya'la al-Mawsili 252:15

Khalaf ibn Hisham al-Bazzar narrated to us, Hammad ibn Zayd narrated to us, from Abu Hazim, from Sahl ibn Sa’d, who said: There was a fight between the Banu ‘Amr ibn ‘Awf, so the Prophet, may Allah bless him and grant him peace, came to them to reconcile between them, and he had already prayed Dhuhr. He said to Bilal: "If the time for ‘Asr prayer arrives and I have not come, then command Abu Bakr to lead the people in prayer." When the time for ‘Asr prayer arrived, Bilal gave the Adhan and the Iqamah, and said: "O Abu Bakr, step forward." So Abu Bakr stepped forward. Then the Messenger of Allah, may Allah bless him and grant him peace, came and split through the rows. When the people saw the Messenger of Allah, may Allah bless him and grant him peace, they clapped—meaning they clapped their hands. It was said that Abu Bakr, when he entered into a prayer, would not turn around. When he saw that the clapping would not cease, he turned around and saw the Messenger of Allah, may Allah bless him and grant him peace, behind him. The Prophet, may Allah bless him and grant him peace, gestured to him to continue. Abu Bakr remained for a moment, praising Allah for the statement of the Messenger of Allah, may Allah bless him and grant him peace, "Continue." Then Abu Bakr walked backward—meaning on his heels. When the Prophet, may Allah bless him and grant him peace, saw that, he stepped forward and led the people in their prayer. When he finished his prayer, he said: "O Abu Bakr, what prevented you from continuing when I gestured to you?" Abu Bakr said: "It is not for the son of Abu Quhafah to lead the Messenger of Allah, may Allah bless him and grant him peace, in prayer." Then he said to the people: "If something happens to you during your prayer, let the men say 'SubhanAllah' (tasbih), and let the women clap."