The Bible treats the tongue extensively in Proverbs and in the Epistle of James.
In James 3:5-6:
5 Even so the tongue is a little member, and boasteth great things. Behold, how great a matter a little fire kindleth! 6 And the tongue is a fire, a world of iniquity: so is the tongue among our members, that it defileth the whole body, and setteth on fire the course of nature; and it is set on fire of hell.
In Proverbs 18:21:
21 Death and life are in the power of the tongue: and they that love it shall eat the fruit thereof.
In Proverbs 15:1:
1 A soft answer turneth away wrath: but grievous words stir up anger.