Matthew 12:35-37
The good man out of the good treasure of his heart brings forth good things, and an evil man out of the evil treasure brings forth evil things.
Hebrews 4:12-13
For the word of God is living and active, sharper than any two-edged sword, piercing even to the division of soul and spirit, of joints and marrow, and discerning the thoughts and intentions of the heart.
James 1:26
If anyone thinks himself to be religious, and yet does not bridle his tongue but deceives his own heart, this man's religion is worthless.
James 3:2-10
For we all stumble in many ways. If anyone does not stumble in what he says, he is a perfect man, able to bridle the whole body as well.