أَخْبَرَنَا قُتَيْبَةُ، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رَكِبَ فَرَسًا فَصُرِعَ عَنْهُ فَجُحِشَ شِقُّهُ الأَيْمَنُ فَصَلَّى صَلاَةً مِنَ الصَّلَوَاتِ وَهُوَ قَاعِدٌ فَصَلَّيْنَا وَرَاءَهُ قُعُودًا فَلَمَّا انْصَرَفَ قَالَ " إِنَّمَا جُعِلَ الإِمَامُ لِيُؤْتَمَّ بِهِ فَإِذَا صَلَّى قَائِمًا فَصَلُّوا قِيَامًا وَإِذَا رَكَعَ فَارْكَعُوا وَإِذَا قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ فَقُولُوا رَبَّنَا لَكَ الْحَمْدُ وَإِذَا صَلَّى جَالِسًا فَصَلُّوا جُلُوسًا أَجْمَعُونَ " .
It was narrated from Anas bin Malik that the Messenger of Allah (PBUH) rode a horse and fell from it, and sustained an injury on his rightside. He led one of the prayers sitting, and we prayed behind him sitting. When he had finished he said: "The Imam is appointed to be followed. If he prays standing then pray standing; when he bows, bow; when he says, Sami' Allahu limanhamidah (Allah hears those who praise Him), say 'Rabbana lakalhamd (Our Lord, to You be praise); and if he prays sitting then pray sitting, all of you." Translation Not Available
Book Ref: Sunan An Nisai Book 10 Hadith 832
Web Ref: Sunan An Nisai Vol 1 Book 10 Hadith 833