The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 843
Anas reported: The Apostle of Allah (may peace be upon him) did not come to us for three days. When the prayer was about to start. Abu Bakr stepped forward (to lead the prayer), and the Apostle of Allah (may peace be upon him) lifted the curtain. When the face of the Apostle of Allah (may peace be upon him) became visible to us, we (found) that no sight was more endearing to us than the face of the Apostle of Allah (may peace be upon him) as it appeared to us. The Apostle of Allah (may peace be upon him) with the gesture of his hand directed Abu Bakr to step forward (and lead the prayer). The Apostle of Allah (may peace be upon him) then drew the curtain, and we could not see him till he died.