Hebrews 12:15 in the King James Version
Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble you, and thereby many be defiled;
Context
14 Follow after peace with all men, and the sanctification without which no man will see the Lord,
15 looking carefully lest there be any man who falls short of the grace of God, lest any root of bitterness springing up trouble you and many be defiled by it,
16 lest there be any sexually immoral person or profane person, like Esau, who sold his birthright for one meal.