That is a very good question, and the answer is that it has not occurred under international law, as far as I know, although international law....
The reason I cited the Rwanda case is that it undercuts the notion that there's never a possibility of prosecuting people for what they have said. The media people and government people were prosecuted for the directions they offered--the instructions, the locations of people--and of course, infamously, at Nuremberg the editor of Der Stürmer magazine was prosecuted and executed solely for what he said. That's why I cited the Rwanda case.
There are, of course, cases around the world of countries that abide human rights having punished people not after the crimes have occurred, but in anticipation of the crimes, in conspiracy-type cases, attempt cases, and solicitation cases. Take, for example, a solicitation case in which somebody offers somebody money to kill an important public official. We obviously don't have to wait until that terrible act of assassination occurs. We do prosecute people for what they have said and the directions they have given, if we're fortunate enough to catch them before the crimes have occurred. We are fortunate enough, because there is a public record of the directions issued by Ahmadinejad and a firm basis for anticipatory conviction without compromise of civil liberties and human rights.