Sahih Muslim 417
Sahih Muslim · Book 4: The Book of Prayers · The Prohibition Of Preceding The Imam In Saying The Takbir Or Anything Else
Abu Huraira reported Allah's Messenger (ﷺ) saying:
حَدَّثَنِي أَبُو الطَّاهِرِ ، حَدَّثَنَا ابْنُ وَهْبٍ ، عَنْ حَيْوَةَ ، أَنَّ أَبَا يُونُسَ ، مَوْلَى أَبِي هُرَيْرَةَ حَدَّثَهُ قَالَ سَمِعْتُ أَبَا هُرَيْرَةَ ، يَقُولُ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم أَنَّهُ قَالَ " إِنَّمَا جُعِلَ الإِمَامُ لِيُؤْتَمَّ بِهِ فَإِذَا كَبَّرَ فَكَبِّرُوا وَإِذَا رَكَعَ فَارْكَعُوا وَإِذَا قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ . فَقُولُوا اللَّهُمَّ رَبَّنَا لَكَ الْحَمْدُ . وَإِذَا صَلَّى قَائِمًا فَصَلُّوا قِيَامًا وَإِذَا صَلَّى قَاعِدًا فَصَلُّوا قُعُودًا أَجْمَعُونَ " .
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.