Hadith 8182

وَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " إِذَا اسْتَيْقَظَ أَحَدُكُمْ مِنْ نَوْمِهِ ، فَلَا يَضَعْ يَدَهُ فِي الْوَضُوءِ حَتَّى يَغْسِلَهَا ، إِنَّهُ لَا يَدْرِي أَحَدُكُمْ أَيْنَ بَاتَتْ يَدُهُ " .
And the Prophet Muhammad (peace and blessings be upon him) said: When any one of you wakes up from his sleep, he should not put his hand into a vessel until he has washed it, for he does not know where his hand was during the night.
Hadith Reference مسند احمد / مسند المكثرين من الصحابة / 8182
Hadith Grading حکم دارالسلام: إسناده صحيح، خ: 162، م: 278