I've heard Al Franken say this on a television interview. He repeated it in an interview with Geov Parrish at WorkingforChange.com (05/02/05) to which we can conveniently link:
GP: What do you think the differences are between you and Limbaugh?
AF: I'm glad you asked me that. I use this example a lot. A few months ago, Rush was talking about the minimum wage. Conservatives like to portray it that no one has to raise a family on the minimum wage, the only people who get the minimum wage are teenagers who want to buy an i-Pod. So Rush says, "75 percent of all Americans on the minimum wage, my friends, are teenagers on their first job." And one of the researchers brings this to me, with a smile, and I say, "Well, can you look it up?" And they look it up, the researcher goes to something called the Bureau of Labor Statistics. 60.1 percent of Americans on minimum wage are twenty and above. 39.9 percent, then, are either teenagers or below twelve (laughs). I had several jobs as a teenager, so you figure, what, 13 percent might be teenagers in their first job. Not 75 percent. So where did Rush get his statistic? Well, he got it directly from his butt. It went out his butt, into his mouth, out the microphone, into the air, into the brains of dittoheads. And they believe this stuff.
So we get our labor statistics from the Bureau of Labor Statistics. He gets his from the Bureau of Rush's Butt. And that's the difference. We don't do that. That's one of the main differences.