Genesis 4:15

15 But the LORD said to him, “Not soa ; anyone who kills Cain will suffer vengeance seven times over.” Then the LORD put a mark on Cain so that no one who found him would kill him.

Read Genesis 4:15 Using Other Translations

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.
Then the LORD said to him, "Not so! If anyone kills Cain, vengeance shall be taken on him sevenfold." And the LORD put a mark on Cain, lest any who found him should attack him.
The LORD replied, “No, for I will give a sevenfold punishment to anyone who kills you.” Then the LORD put a mark on Cain to warn anyone who might try to kill him.