heart

Proverbs 15:2
The tongue of the wise commends knowledge, but the mouth of the fool spouts folly.

Proverbs 16:23
The heart of the wise man instructs his mouth and adds persuasiveness to his lips.

1 Kings 3:23-28
Then the king replied, "This woman says, 'My son is alive and yours is dead, ' but that woman says, 'No, your son is dead and mine is alive.'" . . .

Ecclesiastes 5:2, 6
Do not be hasty to speak, and do not let your heart be hasty to utter a word before God. After all, God is in heaven and you are on earth. So let your words be few. . . .

1 Peter 3:15
But in your hearts sanctify Christ as Lord. Always be prepared to give a defense to everyone who asks you the reason for the hope you possess. But respond with gentleness and respect,

the mouth

Proverbs 10:19
When words are many, sin is unavoidable, but he who restrains his lips is wise.

Proverbs 13:16
Every prudent man acts with knowledge, but a fool displays his folly.

Proverbs 29:11, 20
A fool vents all his anger, but a wise man holds it back. . . .

Ecclesiastes 10:12-14
The words of a wise man's mouth are gracious, but the lips of a fool consume him. . . .

Matthew 12:34
You brood of vipers, how can you who are evil say anything good? For out of the overflow of the heart, the mouth speaks.

Titus 1:10, 11
For many are rebellious and full of empty talk and deception, especially those of the circumcision, . . .

James 3:6-8
The tongue also is a fire, a world of wickedness among the parts of the body. It pollutes the whole person, sets the course of his life on fire, and is itself set on fire by hell. . . .

2 Peter 2:18
With lofty but empty words, they appeal to the sensual passions of the flesh and entice those who are just escaping from others who live in error.