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