Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When one (of you) wakes up, he should not put his hand into the vessel, or he said: into the water, until he has washed it three times, for he does not know where his hand spent the night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1155
Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When one (of you) gets up at night, he should not put his hand into the vessel until he has poured water over it two or three times, for he does not know where his hand spent the night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1156