It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When any of you wakes up from his sleep, let him wash his hands thoroughly before putting them into the water, for no one knows where his hand spent the night!"
(b) This same narration is also reported from Sayyiduna Abu Hurayrah (may Allah be pleased with him) without the repetition.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 201