“Brothers and sisters, do not slander one another. Anyone who speaks against a brother or sister or judges them speaks against the law and judges it. When you judge the law, you are not keeping it,but sitting in judgment on it. 12 There is only one Lawgiver and Judge, the one who is able to save and destroy. But you—who are you to judge your neighbor?” (James 4:11-12)
God gave us His laws so that we would keep them. He did not give us commandments so that we can pass a verdict on our brothers and sisters. God is the only Lawgiver and Judge, and we must be extremely careful to never try to usurp His place. Yes, we can warn our brother about God’s judgment if we see him fall into sin (James 5:20), but we must not act as if we are the judge and jury ourselves. If we have a problem with what our brother is doing we can go to him in person (Matthew 18:15-20), but we should not spread poisonous rumors about him behind his back. We must not treat him like he is spiritually inferior to us, nor should we pretend that we can see into his heart (see I Samuel 16:7).
This verse makes it extremely clear that we should be very careful never to slander another person!