Matthew 7:15-20
Beware of false prophets. They come to you in sheep’s clothing, but inwardly they are ravenous wolves. / By their fruit you will recognize them. Are grapes gathered from thornbushes, or figs from thistles? / Likewise, every good tree bears good fruit, but a bad tree bears bad fruit. ...

James 3:5-6
In the same way, the tongue is a small part of the body, but it boasts of great things. Consider how small a spark sets a great forest ablaze. / The tongue also is a fire, a world of wickedness among the parts of the body. It pollutes the whole person, sets the course of his life on fire, and is itself set on fire by hell.

Matthew 12:34-37
You brood of vipers, how can you who are evil say anything good? For out of the overflow of the heart the mouth speaks. / The good man brings good things out of his good store of treasure, and the evil man brings evil things out of his evil store of treasure. / But I tell you that men will give an account on the day of judgment for every careless word they have spoken. ...

Ephesians 4:29
Let no unwholesome talk come out of your mouths, but only what is helpful for building up the one in need and bringing grace to those who listen.

Psalm 10:7
His mouth is full of cursing, deceit, and violence; trouble and malice are under his tongue.

Romans 3:13-14
“Their throats are open graves; their tongues practice deceit.” “The venom of vipers is on their lips.” / “Their mouths are full of cursing and bitterness.”

Matthew 15:18-19
But the things that come out of the mouth come from the heart, and these things defile a man. / For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, and slander.

James 1:26
If anyone considers himself religious and yet does not bridle his tongue, he deceives his heart and his religion is worthless.

Psalm 36:3
The words of his mouth are wicked and deceitful; he has ceased to be wise and well-doing.

Colossians 3:8
But now you must put aside all such things as these: anger, rage, malice, slander, and filthy language from your lips.

Isaiah 59:3-4
For your hands are stained with blood, and your fingers with iniquity; your lips have spoken lies, and your tongue mutters injustice. / No one calls for justice; no one pleads his case honestly. They rely on empty pleas; they tell lies; they conceive mischief and give birth to iniquity.

1 Peter 3:10
For, “Whoever would love life and see good days must keep his tongue from evil and his lips from deceitful speech.

Psalm 52:2-4
Your tongue devises destruction like a sharpened razor, O worker of deceit. / You love evil more than good, falsehood more than speaking truth. Selah / You love every word that devours, O deceitful tongue.

Luke 6:45
The good man brings good things out of the good treasure of his heart, and the evil man brings evil things out of the evil treasure of his heart. For out of the overflow of the heart the mouth speaks.

Jeremiah 9:3-5
“They bend their tongues like bows; lies prevail over truth in the land. For they proceed from evil to evil, and they do not take Me into account,” declares the LORD. / “Let everyone guard against his neighbor; do not trust any brother, for every brother deals craftily, and every friend spreads slander. / Each one betrays his friend; no one tells the truth. They have taught their tongues to lie; they wear themselves out committing iniquity.