The full quote is:
Americans are free, in short, to disagree with the law but not to disobey it. For in a government of laws and not of men, no man, however prominent or powerful, and no mob, however unruly or boisterous, is entitled to defy a court of law. If this country should ever reach the point where any man or group of men by force or threat of force could long defy the commands of our court and our Constitution, then no law would stand free from doubt, no judge would be sure of his writ, and no citizen would be safe from his neighbors.
Click here to read the full text of President Kennedy’s speech to the nation on the Situation at the University of Mississippi