Abu jahl said to them: "Muhammad alleges that if you follow him you will be kings of the Arabs and the Persians. Then after death you will be raised to gardens like those of the Jordan. But if you do not follow him you will be slaughtered, and when you are raised from the dead you will be burned in the fire of hell." The apostle [Muhammad] came out to them with a handful of dust saying: "I do say that."
Muhammad affirms that those who do not follow him will be slaughtered
On page 222 (326 in the Arabic) of the earliest Muslim biography of Muhammad:
