Genesis 4:13-15

13And Cain said to Jehovah, My punishment is too great to be borne.

14Behold, thou hast driven me this day from the face of the ground, and from thy face shall I be hid; and I shall be a wanderer and fugitive on the earth; and it will come to pass, [that] every one who finds me will slay me.

15And Jehovah said to him, Therefore, whoever slayeth Cain, it shall be revenged sevenfold. And Jehovah set a mark on Cain, lest any finding him should smite him.