Deuteronomy 18:22

Fear him. Septuagint, "you shall not spare him," but cut him off by death. (Haydock) --- Though the completion of what has been foretold be not a sure sign of a true prophecy, (chap. xiii. 2,) yet when the thing does not come to pass which the prophet had spoken unconditionally, he must undoubtedly be rejected; as also when he speaks in the name of false gods. No miracles can then establish his credit. The prophecy of Jonas, and many of the other prophecies, were conditional. (Calmet)