1 Peter 3:15

and sanctify the anointed Lord in your hearts, and be always ready with a defense to every one that asks you a reason for the hope that is in you; but with meekness and fear,

Matthew 12:34

Offspring of vipers, how can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks.

Titus 1:10-11

For there are many disorderly wranglers and deceivers, especially those of the circumcision,

James 3:6-8

And the tongue is a fire, the tongue is made a world of wickedness among our members, it defiles the whole body and sets on fire the course of nature and is set on fire by hell.

2 Peter 2:18

For speaking extravagant words of vanity, they entice with carnal desires of lewdness those scarcely escaped from them, those living 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
and sanctify the anointed Lord in your hearts, and be always ready with a defense to every one that asks you a reason for the hope that is in you; but with meekness and fear,

General references

Matthew 15:18
But the things which proceed from the mouth come from the heart, and these defile the man.