Sayyidah Aishah (may Allah be pleased with her) said: When the Prophet (peace and blessings be upon him) fell ill with the illness in which he (peace and blessings be upon him) passed away, he (peace and blessings be upon him) ordered that Abu Bakr should lead the prayer. Abu Bakr (may Allah be pleased with him) was in the prayer when he (peace and blessings be upon him) came. When Abu Bakr (may Allah be pleased with him) saw him, he began to step back. He (peace and blessings be upon him) gestured: "Lead the prayer." Abu Bakr (may Allah be pleased with him) remained standing, and the Prophet (peace and blessings be upon him) sat beside him; he (peace and blessings be upon him) was leading the prayer, and Abu Bakr (may Allah be pleased with him) was making the people hear his (peace and blessings be upon him) takbir.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5936