Genesis 4:13-15

Cain said to the LORD, “My punishment is greater than I can bear. Behold, You have driven me out this day from the face of the land; and from Your face (presence) I will be hidden, and I will be a fugitive and an [aimless] vagabond on the earth, and whoever finds me will kill me.” And the LORD said to him, “Therefore, whoever kills Cain, a sevenfold vengeance [that is, punishment seven times worse] shall be taken on him [by Me].” And the LORD set a [protective] mark (sign) on Cain, so that no one who found (met) him would kill him. [Gen 4:24]