Musnad Ahmad 1153:52

'Abd al-A'la narrated to us, from Ma'mar, from al-Zuhri, from 'Ubayd Allah ibn 'Abd Allah, from 'A'ishah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) fell ill in the house of Maymunah. He asked his wives for permission to be nursed in my house, and they permitted him. The Messenger of Allah (peace and blessings of Allah be upon him) went out leaning on al-'Abbas and another man, while his feet were dragging on the ground. 'Ubayd Allah said: Ibn 'Abbas said: "Do you know who that man was? He was 'Ali ibn Abi Talib, but 'A'ishah does not feel kindly toward him." Al-Zuhri said: While he was in the house of Maymunah, the Prophet (peace and blessings of Allah be upon him) said to 'Abd Allah ibn Zam'ah: "Command the people to pray." He met 'Umar ibn al-Khattab and said: "O 'Umar, lead the people in prayer." So he led them in prayer. The Messenger of Allah (peace and blessings of Allah be upon him) heard his voice and recognized it, for he was a man with a loud voice. The Messenger of Allah (peace and blessings of Allah be upon him) said: "Is this not the voice of 'Umar?" They said: "Yes." He said: "Allah, the Majestic and Exalted, refuses that, and the believers refuse that. Command Abu Bakr to lead the people in prayer." 'Ubayd Allah ibn 'Abd Allah narrated from 'A'ishah that when he entered the house of 'A'ishah, he said: "Command Abu Bakr to lead the people in prayer." 'A'ishah said: "O Messenger of Allah, Abu Bakr is a tender-hearted man who cannot control his tears, and when he recites the Qur'an, he weeps." She said: "I did not say that except out of dislike that the people would view Abu Bakr with pessimism for being the first to stand in the place of the Messenger of Allah (peace and blessings of Allah be upon him)." He said: "Command Abu Bakr to lead the people in prayer." I argued with him, and he said: "Command Abu Bakr to lead the people in prayer; you are indeed the companions of Yusuf."