It is narrated from Hazrat Mughira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) would stand (in prayer) for such a long time that his blessed feet would swell. People would say, "O Messenger of Allah (peace and blessings be upon him)! Allah Almighty has forgiven all your past and future sins, then why so much effort?" The Noble Prophet (peace and blessings be upon him) would say, "Should I not be a grateful servant?"