Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "The imam is appointed only to be followed, so do not differ from him. When he says the takbir, you too say the takbir; when he bows, you too bow; when he says 'Sami'a Allahu liman hamidah' (Allah hears the one who praises Him), you say 'Allahumma Rabbana lakal-hamd' (O Allah, our Lord, to You belongs all praise); when he prostrates, you too prostrate; and when he prays sitting, you too pray sitting."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5072
(a) Sayyiduna Jabir (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) said the takbir, and Sayyiduna Abu Bakr (may Allah be pleased with him), who was behind him (peace and blessings be upon him), also said the takbir; he was making it heard to us. He (peace and blessings be upon him) saw us standing and gestured to us to sit. When he completed the prayer, he said: "You were about to do what the people of Persia and Rome do for their great men. Follow your imams: if they pray standing, you too pray standing, and if they pray sitting, you too pray sitting."
(b) In the narration of Dawud there are some additional words: The Messenger of Allah (peace and blessings be upon him) led us in prayer, and Sayyiduna Abu Bakr (may Allah be pleased with him) was behind him (peace and blessings be upon him); whenever he (peace and blessings be upon him) said the takbir, Abu Bakr also said the takbir, so as to make it heard to us.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5073
Sayyiduna Jabir (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) fell from his horse onto the trunk of a date palm, and his ankle was dislocated, so he (peace and blessings be upon him) stayed in the house of Sayyidah Aishah (may Allah be pleased with her). We came to visit him (peace and blessings be upon him) in his illness and found him (peace and blessings be upon him) offering a voluntary prayer sitting, while we were standing. Then we came again, and the Prophet (peace and blessings be upon him) was offering an obligatory prayer sitting. We stood behind him (peace and blessings be upon him), and he (peace and blessings be upon him) gestured to us, so we sat down. Then he said: "Follow your imam. If he prays sitting, you too pray sitting, and if he prays standing, you too pray standing; and do not do as the Persians do for their great men."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5074
Al-Sha'bi (may Allah have mercy on him) says that the Messenger of Allah (peace and blessings be upon him) said: "After me, let no one lead the prayer as imam sitting."
Ali bin Umar (al-Daraqutni) said: No one narrated it except Jabir al-Ju'fi, and he is matruk (abandoned). The hadith is mursal, and it cannot serve as proof.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5075