Wading through google news, I can't find a direct quote from Bush that is as juicy as this paraphrasing. I heard this on NPR, and suspect that this phrase is being repeated through some wire service.

Headline: U.S. vows revenge on Iraqis who attack troops
Bush warns that those who believe the attacks on troops will prompt a U.S. withdrawal just don't understand the U.S. commitment. He says the violence will not affect the U.S. resolve, and that the U.S. will stay the course in Iraq.

Bush says the U.S. won't get "nervous" -- and U.S. troops won't leave until Iraq is a free country.

...How the hell does that work? Our troops won't leave Iraq until it's free. That's like saying we won't stop holding your head under water until you breathe.