عَنْ أَبِي هُرَيْرَةَ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ إِذَا اسْتَيْقَظَ أَحَدُكُمْ مِنْ نَوْمِهِ فَلَا يَغْمِسْ يَدَهُ فِي وَضُوئِهِ حَتَّى يَغْسِلَهَا ثَلَاثًا فَإِنَّ أَحَدَكُمْ لَا يَدْرِي أَيْنَ بَاتَتْ يَدُهُ (سنن نسائی : ۱)
Translation
Hazrat Abu Huraira (may Allah be pleased with him) narrated, the Prophet (PBUH) said: "When anyone of you wakes up from his sleep, he should not put his hand into the ablution water until he washes it three times, because none of you knows where his hand spent the night. (Where it kept touching throughout the night.)"