Sunan Abi Dawud Book 2, Hadith 211
the Imam is appointed only to be followed ; so when he prays standing, pray standing, and when he bows, bow; when he raises himself, raise yourselves; when he says “Allah listen to him who praises Him”, “Our Lord ! to Thee be the praise”: and when he prays sitting all of you pray sitting.
Mu’adh b. Jabal would pray along the prophet (ﷺ), then go and lead his people in prayer.
The Messenger of Allah (ﷺ) rode a horse in Medina. It threw him off at the root of a date-palm. His foot was injured. We visited him to inquire about his illness. We found him praying sitting in the apartment of Aisha. We, therefore, stood, (praying) behind him. He kept silent.
We again visited him to inquire about his illness. He offered the obligatory prayer sitting. We, therefore, stood (praying) behind him; he made a sign to us and we sat down. When he finished the prayer, he said: When the imam prays sitting, pray sitting; and when the imam prays standing, pray standing, and do not act as the people of Persia used to act with their chiefs (i.e. the people stood and they were sitting).