Narrated Mu’awiyah (rad): Allah’s Messenger (saW) said:“The eye (when awake) is the string of the anus (to stop air escaping), and if the two eyes sleep the string is untied”. [Reported by Ahmad and At-Tabarani who added,“Whoever sleeps should perform ablution] ”. Also reported by Abu Da’ud mentioning the above addition without the words“the string is untied”, but both versions are weak. And Ibn ‘Abbas (rad) narrated in a Marfu’ (traceable) Hadith that:“Ablution is necessary for one who sleeps while he is lying flat. [Reported by Abu Da’ud and there is weakness in its chain of narrators]