Genesis 4:12

9 And the Lord said to Cain, Where is your brother Abel? And he said, I have no idea: am I my brother's keeper?

10 And he said, What have you done? the voice of your brother's blood is crying to me from the earth.

11 And now you are cursed from the earth, whose mouth is open to take your brother's blood from your hand;

12 No longer will the earth give you her fruit as the reward of your work; you will be a wanderer in flight over the earth.

13 And Cain said, My punishment is greater than my strength.

14 You have sent me out this day from the face of the earth and from before your face; I will be a wanderer in flight over the earth, and whoever sees me will put me to death.

15 And the Lord said, Truly, if Cain is put to death, seven lives will be taken for his. And the Lord put a mark on Cain so that no one might put him to death.