Musnad Abu Ya'la al-Mawsili 118:61

Ishaq narrated to us, Sufyan narrated to us, al-Zuhri narrated to us, from Anas, who said: The last look I looked at the Messenger of Allah, may Allah bless him and grant him peace, was when he pulled back the curtain on the day he died. I looked at his face, and it was as if it were a page of a Mushaf. Then he gestured to the people to remain [in their places], and he let the curtain fall. He passed away at the end of that day, while they were in rows behind Abu Bakr.