Musnad Ahmad 32:723

'Abd al-Razzaq and Muhammad ibn Bakr narrated to us, they said: Ibn Jurayj informed us, Ibn Shihab informed me, from Anas ibn Malik that he said: "The last look I looked at the Messenger of Allah, may Allah bless him and grant him peace, was when he was ill, and he ordered Abu Bakr to lead the people in prayer. The Messenger of Allah, may Allah bless him and grant him peace, pulled back the curtain of 'Aisha's room and looked at the people. I looked at his face, and it was as if it were a page of a Mushaf (copy of the Quran). Abu Bakr retreated on his heels to join the row, thinking that the Messenger of Allah, may Allah bless him and grant him peace, wanted to come out to lead the people in prayer. He (the Prophet) smiled when he saw them in rows, and gestured with his hand to them: 'Complete your prayer.' Then he let down the curtain between him and them, and he passed away on that very day."