Genesis 4:1

Treasury of Scripture Knowledge

And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD.

Adam knew his wife again. She gave birth to a son, and named him Seth, "for God has appointed me another child instead of Abel, for Cain killed him."

I will put enmity between you and the woman, and between your offspring and her offspring. He will bruise your head, and you will bruise his heel."

and he named him Noah, saying, "This same will comfort us in our work and in the toil of our hands, because of the ground which Yahweh has cursed."

unlike Cain, who was of the evil one, and killed his brother. Why did he kill him? Because his works were evil, and his brother's righteous.