Mark 7:21-22
for from the inside, that is, from the hearts of men, designs for doing evil come, sexual immorality, stealing, murder,
Luke 6:45
The good man, out of his good inner storehouse, brings forth what is good, the bad man, out of his bad one, what is bad. For a man's mouth usually speaks the things that fill his heart.
James 1:26
If anyone thinks he is religious, and does not bridle his tongue, but deceives himself, his religious worship is worthless.
James 3:5-8
So the tongue, too, is a little organ but can boast of great achievements. See how a spark, ever so tiny, can set a vast forest on fire!