The Prophet ﷺ said, "When one of you wakes from sleep and wishes to perform ablution, he must not put his hand into the vessel until he has washed it, for he does not know where his hand spent the night."
حدثنا هوذة حدثنا عوف عن محمد
عن النبي ﷺ قال إذا استيقظ أحدكم من نومه فأراد الطهور فلا يضعن يده في الإناء حتى يغسلها فإنه لا يدري أين باتت يده
Its isnad is sahih. It has already appeared at 2780 and also passed by recently. It is found in Bukhari 1/163 no. 162 Fath, and Muslim 1/237 no. 278.