What must the congregation do if the imam is unable to stand during the prayer?

Question : This is an important question. It asks: If the imam is unable to stand during the prayer, such that he prayed and bowed while standing, and then pain struck him in his leg or back and he sat down, do the people sit with him or not?

Answer : We say: No, they do not sit. The evidence for this is that the Prophet (peace and blessings be upon him) appointed Abu Bakr (may Allah be pleased with him) to lead the people in prayer during his final illness. Then one day he came out while the people were praying and advanced until he stood to the left of Abu Bakr, who was standing and completing the prayer. The Prophet (peace and blessings be upon him) completed the prayer with the people while sitting, and the people did not sit. Why?
Because he began the prayer with them while standing. And this hadith, meaning the hadith of the Prophet’s (peace and blessings be upon him) illness, some scholars claimed is an abrogation of his saying: "If he prays standing, pray standing; if he prays sitting, pray sitting." They said that because this occurred during the Prophet’s (peace and blessings be upon him) death-illness, it is later in time and thus abrogates his saying: "If he prays sitting, pray sitting." However, this view is weak for two reasons. The first is that it is an action, and an action does not abrogate a statement, because the indication of a statement regarding the ruling is stronger than the indication of an action, without doubt.
The second is that it is possible to reconcile them, as Imam Ahmad (may Allah have mercy on him) reconciled them by saying that the people did not sit during the Prophet’s (peace and blessings be upon him) death-illness because Abu Bakr began the prayer with them while standing, so the prayer standing was obligatory for them. Do you understand? Yes.