Yes, sometimes our historical figures are misquoted. How do we know about every quote we see? Who is to say that when we research it, the research source is correct? The old adage, "don't believe anything you hear and only half of what you see" comes to mind.

Just for a little test, I just did a search on "Jefferson quotes" and a large amount of stuff came up. At random I just happened to click on this one:

http://www.quotationspage.com/quotes/Thomas_Jefferson/