Deuteronomy 8:19-20

19And it shall be, if thou do at all forget Jehovah thy 1God, and go after other 2gods, and serve them, and bow down to them, I testify against you this day that ye shall utterly perish. 20As the nations which Jehovah is causing to perish before you, so shall ye perish; because ye would not hearken unto the voice of Jehovah your 3God.