Sunan an Nasai
922
Hasan Sahih+2

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

Hasan SahihAbu Ghuddah
Hasan SahihAl-Albani