أَخْبَرَنَا الْجَارُودُ بْنُ مُعَاذٍ التِّرْمِذِيُّ، قَالَ حَدَّثَنَا أَبُو خَالِدٍ الأَحْمَرُ، عَنْ مُحَمَّدِ بْنِ عَجْلاَنَ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِنَّمَا جُعِلَ الإِمَامُ لِيُؤْتَمَّ بِهِ فَإِذَا كَبَّرَ فَكَبِّرُوا وَإِذَا قَرَأَ فَأَنْصِتُوا وَإِذَا قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ فَقُولُوا اللَّهُمَّ رَبَّنَا لَكَ الْحَمْدُ " .
It was narrated that Abu Hurairah said: "The Messenger of Allah (PBUH) said: 'The Imam is appointed to be followed, so when he says the takbir, say the takbir, and when he recites, be silent, and when he says: "Sami' Allahu liman hamidah (Allah hears those who praise Him)," say: "Allahumma rabbana lakal-hamd (Our Lord, to You be praise)." Translation Not Available
Book Ref: Sunan An Nisai Book 11 Hadith 921
Web Ref: Sunan An Nisai Vol 2 Book 11 Hadith 922