Al-Mughirah bin Shu'bah narrated: "Allah's Messenger (S) performed Salat until his feet were swollen, so it was said to him: “You burden yourself like this, while your past and future sins have been forgiven?' He said: “Shouldn't I be a grateful worshipper?””"
SahihSahihHasan SahihBook 2 · Hadith 265