Musnad Ahmad 1153:1899

Al-Zuhri said: Hamzah ibn Abdullah ibn Umar informed me, from Aisha, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) entered my house, he said: "Tell Abu Bakr to lead the people in prayer." I said: "O Messenger of Allah, Abu Bakr is a tender-hearted man; when he recites the Quran, he cannot control his tears. If you were to command someone other than Abu Bakr..." She said: "By Allah, I had no motive other than the dislike that the people would view with pessimism the first person to stand in the place of the Messenger of Allah (peace and blessings of Allah be upon him)." She said: "I repeated the request to him twice or three times, so he said: 'Let Abu Bakr lead the people in prayer, for you are the companions of Yusuf.'"