I guess this is basically the argument from efficient causes, but rephrased in a way that occurred to me in the context of a discussion. Feel free to offer corrections:
If everything is caused, then there is nothing left to be the cause. But if there were no cause, then there would be no effects and therefore nothing would exist. Therefore, there must be two classes of things: On the one hand, that which is caused, and on the other, that which is uncaused. But everything in the universe is caused and therefore goes in the first category. What’s left goes in the second. What exactly is in the second category? Whatever it is, it’s not anything physical or it would be part of the universe. So we’re left with an immaterial, uncaused being who caused the existence of everything in the universe.