Mark 7:21-22
For from within, out of the heart of man proceed evil thoughts, adulteries, fornications, murders,
Luke 6:45
A good man, out of the good treasure of his heart, bringeth forth that which is good; and an evil man, out of the evil treasure of his heart, bringeth forth that which is evil; for of the abundance of the heart the mouth speaketh.
James 1:26
If any one be ever so religious, and bridleth not his tongue, but deceiveth his own heart, this man's religion is vain.
James 3:5-8
So the tongue also is a little member, yet boasteth great things. Behold how much matter a little fire kindleth.