Genesis 4:6-8 New English Translation (NET Bible)
6 Then the Lord said to Cain, “Why are you angry, and why is your expression downcast? 7 Is it not true that if you do what is right, you will be fine? But if you do not do what is right, sin is crouching at the door. It desires to dominate you, but you must subdue it.”
8 Cain said to his brother Abel, “Let’s go out to the field.” While they were in the field, Cain attacked his brother Abel and killed him.