You shall not hate your brother in your heart, but you shall reason frankly with your neighbor, lest you incur sin because of him.
#leviticus 19:17

Don't tolerate sin in a brother's life simply for the sake of peace. Confront evil for the sake of love. On the other hand, don't confront another's sin in a manner that makes you guilty also. Be discrete and kind whenever possible. Most especially, be humble! God commands that we declare his righteous standards. But he doesn't command us to be obnoxious jerks about it all the time.

"A judgmental, critical, slanderous attitude is just as grievous to the Lord as lukewarm living." -Pastor Matt Brown