I haven't been able to google up a transcript from Hardball before the war where he states it, but I found these... I don't think this proves anything though, but it's the best I could do right now.
Is Chris Matthews Liberal or Conservative?: Chris Matthews has been repeatedly accused of being both too liberal and too conservative. In truth, he's an independent thinker whose views are colored more by his Catholic convictions than by political partisanship.
As a young man, he was a conservative Goldwater supporter until he was attracted to the anti-war, pro-civil rights 1968 presidential campaign of fellow Irish Catholic Eugene McCarthy. Matthews has worked for 4 Democratic leaders, and yet, since 2001, has spoken to an array of conservative organizations. Matthews openly states"I'm more conservative than people think... "
Chris Matthews on the Iraq War: Chris Matthews opposed the Iraq War at its inception, and continues to oppose U.S. occupation of Iraq.
http://usliberals.about.com/od/thepressandjournalist1/p/CMatthews.htm
Matthews: ‘I Have Been…Against This Bullshit War From The Beginning’
This morning on Imus, MSNBC’s Chris Matthews blasted the media for not covering the Iraq war. Matthews said that while people are still fighting and dying the Iraq, war “has been taken off television, and Bush must love it.”
Matthews said that most of the media was sold a bill of goods by the Bush administration, but that he’s been “a voice out there against this bullshit war from the beginning.” He added that Cheney was “totally wrong” about Iraq but still “talks like God on television, and we are supposed to believe every word.” Watch it:
MATTHEWS: No. no. no. no. Don. Dono. You can check everything. Get your Nexis-Lexis out. Get your google out. Every column I have written from the day they started talking about Iraq has been against it. Now you are chuckling because you know damn well you’ve pulled my chain here. I have been a voice out there against this bullshit war from the beginning.
IMUS: OK, well, except you then.
MATTHEWS: OK. That’s nicer.
IMUS: Do we have to edit that for the radio, Lou?
PRODUCER: Yeah, we got it.
MATTHEWS: I have never used it ’til now because it was never more appropo. But you are right. The amazing thing is the President is winning now with a hand with nothing in it. They were wrong about the WMD, wrong about the connection to 9/11. Cheney said he didn’t even know there was going to be a war when we went in there. He was totally wrong, and yet he talks like god on television, and we are supposed to believe every word.
http://thinkprogress.org/2006/09/21/matthews-against-war/However, he most likely still had a lot of guests on that talked up the war a lot, so he's not free of complicity.