"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 rule over it.”

Now 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.

9 Then the Lord said to Cain, “Where is your brother Abel?”

“I don’t know,” he replied. “Am I my brother’s keeper?”

The Lord said, “What have you done? Listen! Your brother’s blood cries out to me from the ground."
- Genesis 4: 6-10 (NIV)