Musannaf Ibn Abi Shayba 1:1048

1048. Abd al-Rahim ibn Sulayman narrated to us, from Muhammad ibn Amr, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "When one of you wakes up from his sleep, let him pour over his hand from his vessel three times, for he does not know where his hand spent the night."