Genesis 4:2

And she again bare his brother Abel. This was her second child, her second son, whose name Abel (vanity) indicates that she was feeling the vanity of this earthly life and hoped all the more eagerly for salvation. And Abel was a keeper of sheep, but Cain was a tiller of the ground. Thus the two brothers continued in the calling of their father, the younger son devoting himself to the keeping of the smaller domestic animals and the older to the tilling of the soil.