Narrated Al-Mughira:
The Prophet (ﷺ) used to offer night prayers till his feet became swollen. Somebody said, to him," "Allah has forgiven you, your faults of the past and those to follow." On that, he said, "Shouldn't I be a thankful slave of Allah)?"
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 360
Arabic reference: Book 65, Hadith 4836