Sahih Bukhari Volume 1, Book 11, Hadith Number 680
Narated By ‘Aisha : When the Prophet, became ill in his fatal illness, Someone came to inform him about the prayer, and the Prophet told him to tell Abu Bakr to lead the people in the prayer. I said, “Abu Bakr is a soft-hearted man and if he stands for the prayer in your place, he would weep and would not be able to recite the Qur’an.” The Prophet said, “Tell Abu Bakr to lead the prayer.” I said the same as before. He (repeated the same order and) on the third or the fourth time he said, “You are the companions of Joseph. Tell Abu Bakr to lead the prayer.” So Abu Bakr led the prayer and meanwhile the Prophet felt better and came out with the help of two men; as if I see him just now dragging his feet on the ground. When Abu Bakr saw him, he tried to retreat but the Prophet beckoned him to carry on. Abu Bakr retreated a bit and the Prophet sat on his (left) side. Abu Bakr was repeating the Takbir (Allahu Akbar) of Allah’s Apostle for the people to hear.