Genesis 4:3-5, 15, 25

So it came about in the course of time that Cain brought an offering to the LORD of the fruit of the ground. Abel, on his part also brought of the firstlings of his flock and of their fat portions. And the LORD had regard for Abel and for his offering; but for Cain and for his offering He had no regard. So Cain became very angry and his countenance fell.

So the LORD said to him, “Therefore whoever kills Cain, vengeance will be taken on him sevenfold.” And the LORD appointed a sign for Cain, so that no one finding him would slay him.

Adam had relations with his wife again; and she gave birth to a son, and named him Seth, for, she said, “God has appointed me another offspring in place of Abel, for Cain killed him.”