James 1:26 (KJV)
26If any man among you seem to be religious, and bridleth not his tongue, but deceiveth his own heart, this man's religion is vain.
1 Corinthians 13:1-3 (KJV)
1Though I speak with the tongues of men and of angels, and have not charity, I am become as sounding brass, or a tinkling cymbal. 2And though I have the gift of prophecy, and understand all mysteries, and all knowledge; and though I have all faith, so that I could remove mountains, and have not charity, I am nothing. 3And though I bestow all my goods to feed the poor, and though I give my body to be burned, and have not charity, it profiteth me nothing.
Matthew 12:34-37 (KJV)
34O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh. 35A good man out of the good treasure of the heart bringeth forth good things: and an evil man out of the evil treasure bringeth forth evil things. 36But I say unto you, That every idle word that men shall speak, they shall give account thereof in the day of judgment. 37For by thy words thou shalt be justified, and by thy words thou shalt be condemned.
James 3:8-10 (KJV)
8But the tongue can no man tame; it is an unruly evil, full of deadly poison. 9Therewith bless we God, even the Father; and therewith curse we men, which are made after the similitude of God. 10Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be.
Psalm 62:4 (KJV)
4They only consult to cast him down from his excellency: they delight in lies: they bless with their mouth, but they curse inwardly. Selah.
Isaiah 6 - whole chapter
"For as he thinketh in his heart, so [is] he" -Proverbs 23:7 (KJV)
"There is nothing reliable in what they say; Their inward part is destruction itself. Their throat is an open grave; They flatter with their tongue." -Psalm 5:9 (NASB)
"4Charity suffereth long, and is kind; charity envieth not; charity vaunteth not itself, is not puffed up, 5Doth not behave itself unseemly, seeketh not her own, is not easily provoked, thinketh no evil;" - 1 Corinthians 13:4-5 (KJV)