ʿThe anus, for the eye [in another version of this report, it says, ʿThe eye, for the anus…’ which sounds more apt], is like the string that ties up a waterskin; whoever goes to sleep, let him do wudoo’.”
عَنِ النَّبِيِّ ﷺ قَالَ إِنَّ السَّهَ وِكَاءُ الْعَيْنِ فَمَنْ نَامَ فَلْيَتَوَضَّأْ