Can you help me remember the solution to this riddle?

It went something like this. You are in a new country where there are liars and truth tellers. How can you find out which a new person is with just asking them one question?

I know there is a solution that went something like. “What would you say if I asked you if you were a liar?” But I’m not sure that’s it exactly and if so, why does the answer prove whether the person is a liar or a truth teller.

The logic escapes me.