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’.” (Using translation from Aḥmad 887)
عَنْ رَسُولِ اللهِ ﷺ قَالَ إِنَّمَا الْعَيْنُ وِكَاءُ السَّهِ فَمَنْ نَامَ فَلْيَتَوَضَّأْ