Sayyiduna Abu Musa (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) fell ill, and he (peace and blessings be upon him) said: "Tell Abu Bakr to lead the people in prayer." Sayyidah Aishah (may Allah be pleased with her) said: O Messenger of Allah (peace and blessings be upon him), Abu Bakr (may Allah be pleased with him) is soft-hearted; standing in your (peace and blessings be upon him) place, he will not be able to lead the people in prayer. He (peace and blessings be upon him) said: "Tell Abu Bakr to lead the people in congregation. You are just like the women of Yusuf (peace be upon him)." So Abu Bakr (may Allah be pleased with him) led the people in congregation during the lifetime of the Prophet (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5067