1 John 3:10-12

By this the children of God and the children of the devil are obvious: anyone who does not practice righteousness is not of God, nor the one who does not love his brother. For this is the message which you have heard from the beginning, that we should love one another; not as Cain, who was of the evil one and slew his brother. And for what reason did he slay him? Because his deeds were evil, and his brother’s were righteous.