The Prohibition Of Preceding The Imam In Saying The Takbir Or Anything Else Sahih Muslim 415 a
Translation
Abu Huraira reported
The Messenger of Allah (ﷺ) while teaching us (the principles of faith), said: Do not try to go ahead of the Imam, recite takbir when he recites it, and when he says: "Nor of those who err" you should say Amin, 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".