Musnad Ahmad Hadith 25618

It is narrated from Aisha (may Allah be pleased with her) that during the illness of the Prophet (ﷺ), some people came to the court of Prophethood to visit him. The Prophet (ﷺ) led them in prayer while sitting, and the people began to pray standing. The Prophet (ﷺ) gestured to them to sit down, and after finishing the prayer, he said: The Imam is appointed so that he may be followed; when he bows, you should also bow, and when he raises his head, you should also raise your heads, and when he prays sitting, you should also pray sitting.