Musannaf Ibn Abi Shayba 35:88

Waki’ narrated to us, from al-A’mash, from Abu Sufyan, from Jabir, who said: The Messenger of Allah (may Allah bless him and grant him peace) was thrown from a horse of his, so he fell onto a tree trunk and his foot was dislocated. He said: So we entered upon him to visit him, and he was praying in a loft belonging to ‘A’ishah while sitting. We prayed following his prayer while we were standing, so 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."