The Messenger of Allah ﷺ once prayed while he was ill, so he prayed sitting down, and a group of people prayed behind him standing. He gestured to them to sit. When he finished, he said, "The imam is appointed only to be followed. So when he bows, bow with him, when he rises, rise with him, and when he prays sitting, pray sitting."
و حدثني عن مالك عن هشام بن عروة عن أبيه
صلى رسول الله ﷺ وهو شاك فصلى جالسا وصلى وراءه قوم قياما فأشار إليهم أن اجلسوا فلما انصرف قال إنما جعل الإمام ليؤتم به فإذا ركع فاركعوا وإذا رفع فارفعوا وإذا صلى جالسا فصلوا جلوسا