(a) Aishah (may Allah be pleased with her) says that during the days of his illness the Prophet (peace and blessings be upon him) ordered Abu Bakr (may Allah be pleased with him) to lead the people in prayer, so he (may Allah be pleased with him) continued to lead the people in prayer. Urwah says: The Messenger of Allah (peace and blessings be upon him) felt some relief, so he (peace and blessings be upon him) came out, and Abu Bakr (may Allah be pleased with him) was leading the people as imam. When Abu Bakr (may Allah be pleased with him) saw him, he moved back, but the Prophet (peace and blessings be upon him) gestured: "Stay as you are." The Prophet (peace and blessings be upon him) sat beside Abu Bakr (may Allah be pleased with him). Abu Bakr (may Allah be pleased with him) was praying along with the prayer of the Prophet (peace and blessings be upon him), and the people were praying along with the prayer of Abu Bakr (may Allah be pleased with him).
(b) All these narrations state that the Prophet (peace and blessings be upon him) was the imam and that Abu Bakr (may Allah be pleased with him) and all the people were following him; and in one narration it is reported that Abu Bakr (may Allah be pleased with him) was the imam and the Prophet (peace and blessings be upon him) prayed behind him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5082