Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"The Messenger of Allah (saw) told Abu Bakr to lead the people in prayer when he was sick, and Abu Bakr used to lead them in prayer. Then the Messenger of Allah (saw) began to feel a little better, so he came out, and saw Abu Bakr leading the people in prayer. When Abu Bakr saw him, he stepped back, but the Messenger of Allah (saw) gestured to him to stay where he was. Then the Messenger of Allah (saw) sat beside Abu Bakr. Abu Bakr was following the prayer of the Messenger of Allah (saw), and the people were following the prayer of Abu Bakr." Daif