It is narrated from Hazrat Abu Hurairah (may Allah be pleased with him) in a marfu’ form that when any one of you wakes up from his sleep, he should not put his hand into a vessel until he has washed it three times, for he does not know where his hand was during the night.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 10091