Sunan Abu Dawud, hadith 601

حَدَّثَنَا الْقَعْنَبِيُّ، 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 وَصَلَّيْنَا وَرَاءَهُ قُعُودًا فَلَمَّا انْصَرَفَ قَالَ ‏ "‏ إِنَّمَا جُعِلَ الإِمَامُ لِيُؤْتَمَّ بِهِ فَإِذَا صَلَّى قَائِمًا فَصَلُّوا قِيَامًا وَإِذَا رَكَعَ فَارْكَعُوا وَإِذَا رَفَعَ فَارْفَعُوا وَإِذَا قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ فَقُولُوا رَبَّنَا وَلَكَ الْحَمْدُ وَإِذَا صَلَّى جَالِسًا فَصَلُّوا جُلُوسًا أَجْمَعُونَ ‏"‏ ‏.‏

Anas b. Malik said; The Messenger of Allah (ﷺ) rode a horse and was thrown off it and his right was grazed. He then prayed one of the prayers sitting and we prayed one of the prayers sitting, and when he finished he said:the Imam is appointed only to be followed ; so when he prays standing, pray standing, and when he bows, bow; when he raises himself, raise yourselves; when he says “Allah listen to him who praises Him”, “Our Lord ! to Thee be the praise”: and when he prays sitting all of you pray sitting