Sahih Muslim Book 4, Hadith 83
The Apostle of Allah (ﷺ) fell down from a horse and his right side was grazed. We went to him to inquire after his health when the time of prayer came. He led us in prayer in a sitting posture and we said prayer behind him sitting, and when he finished the prayer hesaid: The Imam is appointed only to be followed; so when he recites takbir, you should also recite that; when he prostrates, you should also prostrate; when he rises up, you should also rise up, and when he said" God listens to him who praises Him," you should say:" Our Lord, to Thee be the praise," and when he prays sitting, all of you should pray sitting.
The Messenger of Allah (ﷺ) said: When the reciter (Imam) utters:" Not of those on whom (is Thine) wrath and not the erring ones," and (the person) behind him utters Amin and his utterance synchronises with that of the dwellers of heavens, all his previous sins would be pardoned.
The Messenger of Allah (ﷺ) fell down from a horse and he was grazed and he led the prayer for us sitting, and the rest of the hadith is the same.