Hadith #371
Arabic Text
وَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنَّمَا جُعِلَ الْإِمَامُ لِيُؤْتَمَّ بِهِ فَلَا تَخْتَلِفُوا عَلَيْهِ وَإِذَا كَبَّرَ فَكَبِّرُوا وَإِذَا رَكَعَ فَارْكَعُوا وَإِذَا قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ فَقُولُوا اللَّهُمَّ رَبَّنَا لَكَ الْحَمْدُ وَإِذَا سَجَدَ فَاسْجُدُوا وَإِذَا صَلَّى جَالِسًا فَصَلُّوا جُلُوسًا أَجْمَعِينَ
English Translation
the Messenger of Allah ﷺ said: 'The imam has been appointed to be followed, so do not differ from him. When he says Allahu Akbar, say Allahu Akbar. When he bows, bow. When he says Sami' Allahu liman hamidah, say Allahumma Rabbana lakal-hamd. When he prostrates, prostrate. And when he prays sitting, all of you pray sitting.'
Quran References
Reference: Musnad Ahmad, Book 18, Hadith 371
Sunnah.com ref: Musnad Ahmad 7809
Islam.wiki ID: IWH-44199