I recently heard that this phrase originated with Arnold Schwarzenegger. Sadly, I haven’t a clue where to go to try and find the commonly attributed source. Where may one find phrase etymology?
Well, there’s a well-known (amongst Jews, at least) Talmudic statement that goes: “Ben Heh Heh says, “According to the pain is the reward.”” So the sentiment, at least, dates back almost 2000 years. I don’t know who gets credit for the specific English verbalization that you’re referring to, though.