(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