Sahih al-Bukhari 7190

It is related that Sahl ibn Sa'd, "There was some fighting between some people of the Banu 'Amr ibn 'Awf. The Prophet, may Allah bless him and grant him peace, heard about that. He prayed Dhuhr and then went to them to make peace among them. When the time for the 'Asr prayer came, Bilal gave the adhan and the iqama and told Abu Bakr to go forward to lead the prayer. The Prophet, may Allah bless him and grant him peace, came while Abu Bakr was praying. He went through the people until he was standing behind Abu Bakr in the row behind him. The people began to clap. When Abu Bakr began the prayer, he would not turn around until he had finished. When he noticed that the clapping was not stopping, he turned and saw the Prophet * behind him. The Prophet, may Allah bless him and grant him peace, indicated to him to carry on, and he indicated with his hand like this. Abu Bakr remained where he was a short time, praising Allah for what the Prophet, may Allah bless him and grant him peace, had said and then went backwards. When the Prophet, may Allah bless him and grant him peace, saw that, he went forward and the Prophet, may Allah bless him and grant him peace, led the people in the prayer. When he finished the prayer, he asked, 'Abu Bakr, what kept you from continuing when I indicated that you should do that?' He answered, 'It is not for Ibn Abi Quhafa to lead the Prophet, may Allah bless him and grant him peace, in prayer.' The Prophet, may Allah bless him and grant him peace, said, 'If something happens, the men should say, "Subhanallah" and the women should clap.'"