“Not so!” replied the LORD. “If anyone slays Cain, then Cain will be avenged sevenfold.” And the LORD placed a mark on Cain, so that no one who found him would kill him.
Jewish Publication Society of America Version (JPS1917) - Genesis 4:15 >And the LORD said unto him: 'Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold.' And the LORD set a sign for Cain, lest any finding him should smite him.