Mark 7:21-22
For from within, out of men's hearts, their evil purposes proceed--fornication, theft, murder, adultery,
Luke 6:45
A good man from the good stored up in his heart brings out what is good; and an evil man from the evil stored up brings out what is evil; for from the overflow of his heart his mouth speaks.
James 1:26
If a man thinks that he is scrupulously religious, although he is not curbing his tongue but is deceiving himself, his religious service is worthless.
James 3:5-8
In the same way the tongue is an insignificant part of the body, but it is immensely boastful. Remember how a mere spark may set a vast forest in flames.