وَعَنْ مُعَاوِيَةَ رضى الله عنه
قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«الْعَيْنُ وِكَاءُ السَّهِ، فَإِذَا نَامَتْ اَلْعَيْنَانِ اِسْتَطْلَقَ اَلْوِكَاءُ»
The Messenger of Allah (sallallahu alayhi wa sallam) 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”.
Bulugh al-Maram 97, Book 1, The Book of Purification, Hadith 97. 1 min read