It was narrated that Abu Hurairah said: The Messenger of Allah (ﷺ) said: 'The Imam is appointed to be followed, so when he says the takbir, say the takbir, and when he recites, be silent, and when he says: Sami' Allahu liman hamidah (Allah hears those who praise Him), say: Allahumma rabbana lakal-hamd (Our Lord, to You be praise).
It was narrated that Abu Hurairah said: The Messenger of Allah (ﷺ) said: 'The Imam is appointed to be followed, so when he says the takbir, say the takbir, and when he recites, be silent.'