Sahih Muslim 278d
Sahih Muslim · Book 2: The Book of Purification · It is disliked for the person who wants to perform wudu’, and others, to put his hand in the vessel (containing water) before washing it three times, if he is not sure whether something impure is on his hands or not
Abu Huraira reported:
وَحَدَّثَنِي سَلَمَةُ بْنُ شَبِيبٍ ، قَالَ حَدَّثَنَا الْحَسَنُ بْنُ أَعْيَنَ ، حَدَّثَنَا مَعْقِلٌ ، عَنْ أَبِي الزُّبَيْرِ ، عَنْ جَابِرٍ ، عَنْ أَبِي هُرَيْرَةَ ، أَنَّهُ أَخْبَرَهُ أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " إِذَا اسْتَيْقَظَ أَحَدُكُمْ فَلْيُفْرِغْ عَلَى يَدِهِ ثَلاَثَ مَرَّاتٍ قَبْلَ أَنْ يُدْخِلَ يَدَهُ فِي إِنَائِهِ فَإِنَّهُ لاَ يَدْرِي فِيمَ بَاتَتْ يَدُهُ " .
The Apostle of Allah (ﷺ) said: When anyone amongst you wakes up from sleep, he should wash his hands three times before putting it in the utensil, for he does not know where his hand was during the night.