Genesis 4:3-5

4:3 At the designated time Cain brought some of the fruit of the ground for an offering to the Lord. 4:4 But Abel brought some of the firstborn of his flock – even the fattest of them. And the Lord was pleased with Abel and his offering, 4:5 but with Cain and his offering he was not pleased. So Cain became very angry, and his expression was downcast.

Genesis 4:15

4:15 But the Lord said to him, “All right then, if anyone kills Cain, Cain will be avenged seven times as much.” Then the Lord put a special mark on Cain so that no one who found him would strike him down.

Genesis 4:25

4:25 And Adam had marital relations with his wife again, and she gave birth to a son. She named him Seth, saying, “God has given me another child in place of Abel because Cain killed him.”