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?" (ES)
English reference (ES): Book 39, Hadith 250 (ES)
Arabic reference (ES): Book 40, Hadith 263 (ES)