Hadith 110
Sayyiduna Abdullah bin Mas'ud, may Allah be pleased with him, says that the Noble Prophet, peace and blessings be upon him, used to pray at night so much that his feet would swell. It was said: O Messenger of Allah! Has Allah not forgiven your past and future sins? He, peace and blessings be upon him, said: "Then should I not be a grateful servant of Allah?"