Anas ibn Mālik (may Allah be pleased with him) reported: The Prophet (ﷺ) ﷺ fell from a horse and suffered abrasions on his right side. We went to visit him and when the time of prayer came, he led us in prayer sitting down, and we prayed sitting. When he concluded the prayer he said: “The imam is appointed only to be followed. When he says Allāhu Akbar, say Allāhu Akbar; when he bows, bow.” Sufyān added on one occasion: “when he prostrates, prostrate; and when he says Samiʿa Allāhu liman ḥamidah, say Rabbanā wa laka'l-ḥamd; and if he prays sitting, then all of you pray sitting.” Reference: Musnad Aḥmad 154