Hebrews 12:14-15 (NKJV)
"Pursue peace with all people, and holiness, without which no one will see the Lord: 15 looking carefully lest anyone fall short of the grace of God; lest any root of bitterness springing up cause trouble, and by this many become defiled;"
Ephesians 4:31 (NKJV)
"And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption. Let all bitterness, wrath, anger, clamor, and evil speaking be put away from you, with all malice."