Leading the prayer while seated on a chair with the congregation standing

Question:
Honorable Shaykh, may Allah grant you success. A questioner says: Is it valid for the imam to pray while sitting on a chair while the ma'mum (congregation) behind him are standing?

Answer:
No, this is not valid. One who is unable to perform a pillar of the prayer is not to be followed in prayer. I say that it is not permissible to pray behind one who is sitting on a chair or on the ground, except for the imam of the locality. By "imam of the locality" I mean the regular imam whose excuse is expected to end, provided these two conditions are met: that he is the regular imam of the mosque, and that his excuse is expected to end. In that case, they pray behind him and sit down. If he begins the prayer sitting, they pray behind him sitting. If he begins standing and then an excuse befalls him and he sits, they complete their prayer standing. The Messenger (peace and blessings be upon him) said: .
Yes. When the Prophet (peace and blessings be upon him) fell ill, Abu Bakr began the prayer for the people. Then the Prophet (peace and blessings be upon him) came and entered, and stood to the left of Abu Bakr. Abu Bakr became a ma'mum, and the Messenger became the imam. They prayed behind the Messenger (peace and blessings be upon him) standing. Yes.