The book of Proverbs is a constant go-to devotional book for me. Proverbs has much to tell me about controlling my mouth.
Those who guard their mouths preserve their lives; those who open wide their lips come to ruin.
A fool takes no pleasure in understanding, but only in expressing personal opinion.
The words of the mouth are deep waters; the fountain of wisdom is a gushing stream.
A fool’s lips bring strife, and a fool’s mouth invites a flogging.
The mouths of fools are their ruin, and their lips a snare to themselves.
The words of a whisperer are like delicious morsels; they go down into the inner parts of the body.
Death and life are in the power of the tongue, and those who love it will eat its fruits.
A word fitly spoken is like apples of gold in a setting of silver.
Proverbs 13:3; 18:2, 4, 6–8, 21; 25:11
(From Richard Foster, Year with God: Living Out the Spiritual Disciplines