Sahih Muslim

Abu Huraira reported Allah's Messenger (ﷺ) saying:The Imam is appointed to be followed. So recite takbir when he recites it, and bow down when he bows down and when he utters:"" Allah listens to him who praises Him,"" say"" O Allah, our Lord, for Thee be the praise."" And when he prays, standing, you should pray standing. And when he prays sitting, all of you should pray sitting