The ruling on praying behind an imam who is unable to stand

Question:
If the imam is unable to prostrate, is the prayer valid behind this imam who is unable?

Answer:
If he is the regular imam of the congregation. Yes. And if he is struck by an illness that prevents him from standing, and he prays sitting down, starting the prayer with them while sitting, then they pray behind him sitting down. The saying of the Prophet (peace and blessings be upon him) , this is regarding the regular imam of the congregation whose illness is expected to end. So if he prays sitting down due to illness, then they pray behind him; if he starts the prayer sitting down, they pray behind him sitting down.
And if he starts the prayer standing, and then an illness strikes him that prevents him from standing, then they continue standing behind him and do not sit down. He sits down due to the excuse, and they complete their prayer standing, because they started the prayer standing, and what happened to the imam happened, so he sat down because of the excuse. Then they continue praying standing and do not sit down. As for if the regular imam of the congregation is ill and his illness is expected to end, and he starts the prayer with them sitting down, then they sit down behind him, as happened with the Prophet (peace and blessings be upon him) when he was ill; he prayed sitting down, and they prayed behind him sitting down. Yes.