It is narrated from Sayyida Aisha (may Allah be pleased with her), she says that when the Messenger of Allah (peace and blessings be upon him) used to pray at night, he would stand for so long that his feet would become swollen. So one day she said: O Messenger of Allah! Why do you stand for so long, when all your past and future sins have been forgiven? The Prophet (peace and blessings be upon him) replied: O Aisha! Should I not be a most grateful servant?