Sahih Muslim Book 4, Hadith Number 837.

‘Aisha reported: When the Messenger of Allah (may peace be upon him) was confined to bed, Bilal came to him to summon him to prayer. He (the Holy Prophet) said: Ask Abu Bakr to lead the people in prayer. She (‘Aisha) reported: I said: Messenger of Allah, Abu! Bakr is a tender-hearted man, go when he would stand at your place (he would be so overwhelmed by feelings) that he would not be able to make the people hear anything (his recitation would not be audible to the followers in prayer). You should better order Umar (to lead the prayer). He (the Holy Prophet) said: Ask Abu Bakr to lead people in prayer. She (‘Aisha) said: I asked Hafsa to (convey) my impression to him (the Holy Prophet) that Abu Bakr was a tender-hearted man, so when he would stand at his place, he would not be able to make the people bear anything. He better order Umar. Hafsa conveyed this (message of Hadrat ‘Aisha) to him (the Holy Prophet). The Messenger of Allah (may peace be upon him) said: (You are behaving) as if you are the females who had gathered around Yusuf. Order Abd Bakr to lead the people in prayer. She (‘Aisha) reported: So Abu Bakr was ordered to lead the people in prayer. As the prayer began, the Messenger of Allah (may peace he upon him) felt some relief; he got up and moved supported by two persons and his feet dragged on earth (due to excessive weakness). ‘Aisha reported: As he (the Holy Prophet) entered the mosque. Abu Bakr perceived his (arrival). He was about to with. draw, but the Messenger of Allah (may peace be upon him) by the gesture (of This hand) told him to keep standing at his place. The Messenger of Allah (may peace be upon him) came and seated himself on the left side of Abu Bakr. She (‘Aisha) reported: The Messenger of Allah (may peace be upon him) was leading people in prayer sitting. Abu Bakr was following the prayer of the Apostle (may peace be upon him) in a standing posture and the people were following the prayer of Abu Bakr.