Anas Radiyallahu 'Anhu narrates:
"The last glimpse I had of Rasulullah Sallallahu 'Alayhi Wasallam was at the time of his last illness on a Monday morning when he lifted the curtain of his house (to take a look at his ummah performing the salaah). At that time his mubaarak face was shining and clear as if it was a page of the Mus-haf (Qur-aan). At that time the people were performing the (fajr) salaah behind Abubakr Radiyallahu 'Anhu. The people began moving back (in happiness after seeing him, thinking that he would come to join them. Before this too on an occasion when Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam became ill, Abubakr Radiyallahu 'Anhu led the salaah. When he was recovering he would come and join the congregational prayer). Rasulullah Sallallahu 'Alayhi Wasallam made a sign to the people to remain in their places. Rasulullah Sallallahu 'Alayhi Wasallam passed away on that day".
English reference: Book 53, Hadith 368
Arabic reference: Book 54, Hadith 385