It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) rode a horse, then fell from it, and his right side was grazed. So the Prophet (peace and blessings of Allah be upon him) performed the prayer sitting, and we also performed the prayer sitting behind him. Then when the Prophet (peace and blessings of Allah be upon him) finished the prayer, he said: "The Imam is appointed so that he may be followed. So when the Imam prays standing, you should also pray standing, and when the Imam bows (in ruku‘), you should also bow, and when the Imam raises his head, you should also raise your heads, and when the Imam says «سَمِعَ اللّٰهُ لِمَنْ حَمِدَهُ» , you should say «رَبَّنَا وَلَكَ الْحَمْدُ» , and when the Imam prays sitting, you should also pray sitting."