Ibn Hibban

Sayyiduna Jabir (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) rode a horse in Madinah Munawwarah and fell from it onto the trunk of a date-palm tree, due to which he sprained his foot. We came to visit him to inquire about his health and found him in the upper room of Sayyidah Aisha (may Allah be pleased with her). He was performing voluntary prayers while sitting. We stood behind him, so he moved away from us. Then, when we visited him a second time, we found him performing an obligatory prayer. We stood behind him, so he gestured to us, and we sat down. When he completed the prayer, he said: "When the Imam performs the prayer sitting, you should also perform the prayer sitting. When he performs the prayer standing, you should also perform the prayer standing. Do not do as the people of Persia do for their kings." (Imam Ibn Hibban, may Allah have mercy on him, says:) In this narration, there is a clear statement regarding the words transmitted from Humaid, in which it is mentioned that the Prophet (peace and blessings be upon him) led them in prayer while sitting, and they were standing. This was a voluntary prayer. When the time for the obligatory prayer came, the Prophet (peace and blessings be upon him) instructed them to perform the prayer sitting, just as the Prophet (peace and blessings be upon him) performed the prayer. So this matter becomes the most emphasized. (And it proves) that the command of the Prophet (peace and blessings be upon him) which we have mentioned is a command of obligation, not a command for expressing virtue.