Proverbs 16:27-30 (ESV)
27 A worthless man plots evil,
and his speech is like a scorching fire.
28 A dishonest man spreads strife,
and a whisperer separates close friends.
29 A man of violence entices his neighbor
and leads him in a way that is not good.
30 Whoever winks his eyes plans dishonest things;
he who purses his lips brings evil to pass.
James 3:6-9 (ESV)
6 And the tongue is a fire, a world of unrighteousness. The tongue is set among our members, staining the whole body, setting on fire the entire course of life, and set on fire by hell. 7 For every kind of beast and bird, of reptile and sea creature, can be tamed and has been tamed by mankind, 8 but no human being can tame the tongue. It is a restless evil, full of deadly poison. 9 With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God.