Sunan Abi Dawud Book 2, Hadith 216
when the prophet (ﷺ) became seriously ill, we prayed behind him while he was sitting and Abu Bakr was calling “Allah is most great “ to cause the people to hear the TAKBIR. Then he (the narrators) narrated the rest of the tradition.
The IMAM is appointed only to be followed; so when he prays standing. Pray standing ; and when he raises himself, raise yourself: and when he prays sitting. Pray sitting.
Messenger of Allah, our Imam is ill. He said : When he prays sitting, pray sitting.
Abu Dawud said : The chain of this tradition is not continuous (muttasil)