Mark 7:21-22
For it is from within, out of the hearts of men, that there come evil thoughts--unchastity, theft, murder, adultery,
Luke 6:45
A good man, from the good stores of his heart, brings out what is good; while a bad man, from his bad stores, brings out what is bad. For what fills a man's heart will rise to his lips.
James 1:26
When a man appears to be religious, yet does not bridle his tongue, but imposes upon his own conscience, that man's religious observances are valueless.
James 3:5-8
So is it with the tongue. Small as it is, it is a great boaster. Think how tiny a spark may set the largest forest ablaze!