"Set a watch, O Lord , before my mouth; keep the door of my lips." -Psalm 141:3, KJV.
God can keep us from saying many things that we really shouldn't (whether they're wrong, hurtful, or just unnecessary). As humans, we are fallible and have a sin nature. James tells us that the tongue is the hardest part of the body to tame. Fortunately, we are not alone. God will gladly help us guard our mouths if we'll let Him.