Genesis 4:15

4:15 Yahweh said to him, "Therefore whoever slays Cain, vengeance will be taken on him sevenfold." Yahweh appointed a sign for Cain, lest any finding him should strike him.
-World English Bible

Other Translation

4:15 And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him.
-King James Version