Genesis 4:2-4

4:2 Then she gave birth to his brother Abel. Abel took care of the flocks, while Cain cultivated the ground.

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,