(a) It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When any of you wakes up, let him pour water over his hands three times before putting his hand into the vessel, for what does he know of how his hand spent the night?"
(b) In (another) narration from Sayyiduna Abu Hurayrah (may Allah be pleased with him) it is: "Let him pour water over his hand."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 212