Re: “ISIS has nothing to do with Islam”.
OK, lets take a step back 
Your original question is *“ISIS has nothing to do with Islam. How to prove this to someone who thinks otherwise?”
*I am assuming that your question is non-rhetorical and you are sincere about proving the above. As a non-Muslim, I am telling you what prevents non-Muslims from believing that ISIS is not equal to Islam. I don’t think many Muslims will be able to give you a non-Muslim perspective. No need to get all defensive on me.