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 Sahih Muslim 278d
Arabic hadith text
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 " .
Translation
Abu Huraira reported
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.