Sahih Muslim Book 4, Hadith 92
The Messenger of Allah (ﷺ) said: The Imam is appointed, so that he should be followed, so don't be at variance with him. Recite takbir when he recites it; bow down when he bows down and when he says:" Allah listens to him who praises Him," say:" O Allah, our Lord, to Thee be the Praise." And when he (the Imam) prostrates, you should also prostrate, and when he says prayer sitting, you should all observe prayer sitting.
The Messenger of Allah (ﷺ) led the prayer and Abu Bakr was behind him. When the Messenger of Allah (ﷺ) recited the takbir, Abu Bakr also recited (it) in order to make it audible to us. And the rest of the hadith is like one transmitted by Laith.
A hadith like this has been transmitted by Hammam b. Munabbih from the Messenger of Allah (ﷺ) on the authority of Abu Huraira.