Sunan Ibn Majah Book 1, Hadith 130
"'Ali called for water, and he washed his hands before putting them in the vessel, then he said: 'This is what I saw the Messenger of Allah doing.'"
"The Messenger of Allah said: 'When anyone of oyu gets up from sleep and wants to perform ablution, he should not put his hand into the vessel he used for ablution until he has washed it, because he does not know where his hand spent the night or where he put it.'"
The Messenger of Allah said: "There is no ablution for one who does not mention the Name of Allah (before doing it)."