1 Peter 3:15

but sanctify the Lord God in your hearts: and be always ready with your reply to every man who demands a reason respecting the hope which is in you with meekness and fear:

Matthew 12:34

Ye broods of vipers, how can ye speak good things, yourselves being wicked? for out of the abundance of the heart the mouth speaketh.

Titus 1:10-11

For there are many disorderly persons vainly talkative, and under a spirit of delusion, especially some of the circumcised;

James 3:6-8

And the tongue is a fire, a world of iniquity: in such manner is the tongue placed among our members, that it defileth all the body, and setteth on fire the circle of nature; and is set on fire of hell.

2 Peter 2:18

Uttering pompous discourses of inanity, ensnaring by the lusts of the flesh, by lascivious impurities, those who had truly escaped from such as live in a course of delusion.

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 sanctify the Lord God in your hearts: and be always ready with your reply to every man who demands a reason respecting the hope which is in you with meekness and fear:

General references

Matthew 15:18
But the things which go forth out of the mouth, come out of the heart, and they are the things which defile a man: