It wasnarrated that Abu Hurairah said:
"The Messenger of Allah (ﷺ)usedto pray until his feet became swollen. It was said: 'O MessengerofAllah, Allah has forgiven you your past and future sins.' He said:'Should I not be a thankful slave?'" (FR)
English reference (FR): Vol. 1, Book 5, Hadith 1420 (FR)
Arabic reference (FR): Book 5, Hadith 1485 (FR)