Genesis 4:13-15

Cain said to the LORD, “My punishment is more than I can bear. Today you are driving me from the land, and I will be hidden from your presence; I will be a restless wanderer on the earth, and whoever finds me will kill me.” But the LORD said to him, “Not so; 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.