Hebrews 12:15
Take heed, that no man fall away from the grace of God: let no root of bitterness spring up and trouble you, lest thereby many be defiled.
Proverbs 11:12 Geneva
He that despiseth his neighbor, is destitute of wisdom: but a man of understanding will keep silence.
LXX
A person who lacks sense scorns citizens, but an intelligent man keeps quiet.
Proverbs 12:18 LXX
Some, when they speak, wound with a dagger, but the tongues of wise men heal.
James 3:10-16
Out of one mouth proceedeth blessing and cursing: my brethren, these things ought not so to be. Doth a fountain send forth at one place sweet water and bitter? Can the fig tree, my brethren, bring forth olives, either a vine figs? so can no fountain make both salt water and sweet.
Who is a wise man and endued with knowledge among you? let him show by good conversation his works in meekness of wisdom. But if ye have bitter envying and strife in your hearts, rejoice not, neither be liars against the truth. This wisdom descendeth not from above, but is earthly, sensual, and devilish. For where envying and strife is, there is sedition, and all manner of evil works.
Acts 8:20-24
Then said Peter unto him, Thy money perish with thee, because thou thinkest that the gift of God may be obtained with money. Thou hast neither part nor fellowship in this business: for thine heart is not right in the sight of God. Repent therefore of this thy wickedness, and pray God, that if it be possible, the thought of thine heart may be forgiven thee. For I see that thou art in the gall of bitterness, and in the bond of iniquity. Then answered Simon, and said, Pray ye to the Lord for me, that none of these things which ye have spoken, come upon me.
Romans 3:14-18
Whose mouth is full of cursing and bitterness. Their feet are swift to shed blood. Destruction and calamity are in their ways: And the way of peace they have not known. The fear of God is not before their eyes.
Ephesians 4:29-32
Let no corrupt communication proceed out of your mouths: but that which is good to the use of edifying, that it may minister grace unto the hearers. And grieve not the holy Spirit of God, by whom ye are sealed unto the day of redemption. Let all bitterness, and anger, and wrath, crying, and evil speaking be put away from you, with all maliciousness. Be ye courteous one to another, and tender hearted, freely forgiving one another, even as God for Christ’s sake, freely forgave you.
Colossians 3:8-10
But now put ye away even all these things, wrath, anger, maliciousness, cursed speaking, filthy speaking, out of your mouth. Lie not one to another: seeing that ye have put off the old man with his works, And have put on the new, which is renewed in knowledge after the image of him that created him,
Proverbs 12:13 LXX
Through the sin of his lips a sinner falls into snares, but a just person escapes from them.