It is narrated from Sayyiduna Muawiyah bin Abi Sufyan (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Indeed, the eyes are the tie of the anus, so when the eyes sleep, the tie is loosened." Imam Darimi was asked: Do you also say this? He replied: No, if someone falls asleep while standing, his ablution will not be broken.