Abu Dawud Book 1, Hadith Number 103.

Chapter : A man who puts his hands in the utensil before washing it.

Narated By Abu Hurairah : The Messenger of Allah (PBUH) said: When anyone amongst you wakes up from sleep at night, he should not put his hand in the utensil until he washed his hand three times, for he does not know where his hand was during the night.