Who said if you disagree with President Obama you are racist?

This is a popular gripe said by republicans so I would love to know who said this. Please no answers of people you know personally. This is such a hot topic on fox news, and they dont know the people you know personally. They must be talking about people they hear on TV, the news etc. Famous people that I am able to google and find. Please no Jimmy Carter answers either because he did not say this. If you listen to his whole speech. He said the extreme fringe making personal attacks on Obama. (not everyone that disagree). All Im asking for is a little proof that an educated person said this. I cant prove that your co-worker said it.