Isaiah 22:14

And It was revealed In mine ears by the Lord of hosts, who, in His word to the prophet, makes Himself known, reveals His will, Surely this iniquity shall not be purged from you till ye die, death being the sentence of God upon the willful sinner, saith the Lord God of hosts. The idea of death, eternal death, as a form of punishment, is by no means found only in the New Testament, but is plainly shown in the Old Testament as well.