It is narrated from Sayyiduna Abu Juhayfah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) would pray so much that his (peace and blessings be upon him) blessed feet would swell. It was said: O Messenger of Allah! Allah has forgiven you all your past and future sins. He (peace and blessings be upon him) said: "Should I not be a grateful servant?"
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18572