أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، وَحُمَيْدُ بْنُ مَسْعَدَةَ، قَالاَ حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، قَالَ حَدَّثَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ إِذَا اسْتَيْقَظَ أَحَدُكُمْ مِنْ مَنَامِهِ فَلاَ يُدْخِلْ يَدَهُ فِي الإِنَاءِ حَتَّى يُفْرِغَ عَلَيْهَا ثَلاَثَ مَرَّاتٍ فَإِنَّهُ لاَ يَدْرِي أَيْنَ بَاتَتْ يَدُهُ ‏"‏ ‏.‏

It was narrated from Abu Hurairah that the Messenger of Allah (PBUH) said: "When any one of you wakes from sleep, let him not put his hand into the vessel until he has washed it three times, because he does not know where his hand spent the night." Translation Not Available

Book Ref: Sunan An Nisai Book 1 Hadith 161
Web Ref:  Sunan An Nisai Not Available