Musnad Ahmad 1017:125

'Abd al-Samad ibn 'Abd al-Warith narrated to us, Za'idah narrated to us, 'Abd al-Malik ibn 'Umayr narrated to us, from Ibn Buraydah, from his father, who said: The Messenger of Allah (may Allah bless him and grant him peace) became ill, so he said: "Command Abu Bakr to lead the people in prayer." 'Aishah said: "O Messenger of Allah, my father is a soft-hearted man." He said: "Command Abu Bakr to lead the people in prayer, for you are the companions of Yusuf." So Abu Bakr led the people in prayer, while the Messenger of Allah (may Allah bless him and grant him peace) was still alive.