Genesis 4:2-5 - Now Abel kept flocks, and Cain worked the soil. In the course of time Cain brought some of the fruits of the soil as an offering to the Lord. But Abel brought fat portions from some of the firstborn of his flock. The Lord looked with favor on Abel and his offering, but on Cain and his offering he did not look with favor. So Cain was very angry, and his face was downcast.
Genesis 4:6-8 - Then the Lord said to Cain, “Why are you angry? Why is your face downcast? If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it. Now Cain said to his brother Abel, “Let’s go out to the field.” And while they were in the field, Cain attacked his brother Abel and killed him.