Genesis 4:13-16New International Version (NIV)

13 Cain said to the Lord, “My punishment is more than I can bear. 14 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.”

15 But the Lord said to him, “Not so[a]; 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. 16 So Cain went out from the Lord’s presence and lived in the land of Nod,[b] east of Eden.

Leviticus 17:11New International Version (NIV)

11 For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one’s life.[a]