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
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.