It is also narrated from Abu Hurayrah Radiyallahu 'Anhu that Rasulullah Sallallhu 'Alayhi Wasallam performed such a long salaah that his mubaarak legs became swollen. He was asked:
"You perform such long prayers, whereas all your past and future sins have been forgiven?. "Rasulullah Sallallhu 'Alayhi Wasallam replied: "Should I not be an appreciative servant?"
English reference: Book 39, Hadith 250
Arabic reference: Book 40, Hadith 263