عَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ: ((إِنَّ الْعَيْنَ وَكَاءُ السَّهْوِ فَمَنْ نَامَ فَلْيَتَوَضَّأْ))
It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him and his family) said: Surely, the eye is a strap for the anus, so whoever sleeps should perform ablution.