Musannaf Ibn Abi Shayba 3:4759

Waki’ narrated to us, he said: Al-A’mash narrated to us, from Abu Sufyan, from Jabir, who said: The Prophet (peace and blessings of Allah be upon him) was thrown from a horse of his, so he fell onto the trunk of a palm tree and his foot was dislocated. We entered upon him to visit him while he was praying in a loft belonging to Aisha. We prayed following his prayer while we were standing. Then we entered upon him another time while he was praying sitting, so we prayed following his prayer while we were standing. He gestured to us to sit. When he finished praying, he said: "The Imam was only appointed to be followed. So if he prays standing, then pray standing, and if he prays sitting, then pray sitting. And do not stand while he is sitting, as the people of Persia do with their dignitaries."