وَعَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ
قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا اسْتَيْقَظَ أَحَدُكُمْ مِنْ نَوْمِهِ فَلَا يَغْمِسْ يَدَهُ فِي الْإِنَاءِ حَتَّى يَغْسِلَهَا فَإِنَّهُ لَا يَدْرِي أَيْنَ بَاتَتْ يَدُهُ»
The Prophet (sallallahu alayhi wa sallam) said:, “When one of you awakes from sleep he must not dip his hand in the vessel till he has washed it three times, for he does not know where his hand was during the night.”
Mishkat al-Masabih 364, Book 4, Purification, Hadith 100. 1 min read