Deuteronomy 18:20 in the King James Version
But the prophet, which shall presume to speak a word in my name, which I have not commanded him to speak, or that shall speak in the name of other gods, even that prophet shall die.
Context
19 It shall happen, that whoever will not listen to my words which he shall speak in my name, I will require it of him.
20 But the prophet who speaks a word presumptuously in my name, which I have not commanded him to speak, or who speaks in the name of other gods, that same prophet shall die.”
21 You may say in your heart, “How shall we know the word which the LORD has not spoken?”