1 Peter 3:15

but in your hearts be consecrated to Christ as Lord, and always be ready to make your defense to anyone who asks a reason for the hope you have. But you must do it in gentleness and reverence,

Matthew 12:34

You brood of vipers! How can you, wicked as you are, say anything that is good? For the mouth talks about the things that fill the heart.

Titus 1:10-11

For there are many insubordinate people, mere talkers with nothing to say, but deceivers of their own minds, especially those of the circumcision party,

James 3:6-8

And the tongue is a fire, and takes its place among the parts of our bodies as a world of evil; it soils the whole body and sets on fire the circle of man's nature, and itself is set on fire by hell.

2 Peter 2:18

For by uttering arrogant nonsense, through base desires of the lower nature, they entice into immorality men who are just escaping from those who live in error,

Treasury of Scripture Knowledge

Summary

The heart of the righteous studieth to answer: but the mouth of the wicked poureth out evil things.

Heart

General references

Bible References

Heart

1 Peter 3:15
but in your hearts be consecrated to Christ as Lord, and always be ready to make your defense to anyone who asks a reason for the hope you have. But you must do it in gentleness and reverence,

General references

Matthew 15:18
But the things that come out of the mouth come from the heart, and they make the man foul.