The Mother of the Believers Sayyidah Aishah (may Allah be pleased with her) narrates that during the days of his illness the Messenger of Allah (peace and blessings be upon him) prayed sitting, and the Companions prayed behind him standing, so he gestured to them to sit. When he had finished the prayer, he said: "The imam is appointed only to be followed. When he bows, you bow; when he raises his head from bowing, you raise your heads; and when he leads the prayer sitting, you pray sitting."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3413