Musannaf Ibn Abi Shaybah 7323 — The imam praying sitting

Sayyiduna Anas (may Allah be pleased with him) said: The Prophet (peace and blessings be upon him) fell from a horse and his right side was injured. We came to visit him, and the time of prayer arrived. The Prophet (peace and blessings be upon him) led us in prayer sitting, and we also prayed sitting behind him. When he (peace and blessings be upon him) completed the prayer, he said: "The imam is appointed only to be followed. When he says the takbir, you say the takbir too; when he bows, you bow too; when he says 'Sami'a Allahu liman hamidah' (Allah hears the one who praises Him), you say 'Rabbana wa laka al-hamd' (Our Lord, and to You belongs all praise). When he prays sitting, then all of you pray sitting."