The Prophet said, The Imam is to be followed. Say the Takbir when he ...

Hadith 1:701

Narrated Abu Huraira:

The Prophet said, "The Imam is to be followed. Say the Takbir when he says it; bow if he bows; if he says 'Sami a-l-lahu Liman hamida', say, ' Rabbana wa-laka-l-hamd', prostrate if he prostrates and pray sitting altogether if he prays sitting."