The plans of the heart belong to man, but the answer of the tongue is from the LORD.
Proverbs 16:1 ESV

Does this mean that God controls what we say? Here are some alternative interpretations:

The state of a man's heart eventually reveals itself through his speech no matter how eloquent and deceitful he might be.

God knows what a man is planning and rebukes him before he begins.

Whatever a man thinks in his own head is his own business, but the moment it comes out into the world, it becomes God's business too, and the man will be judged by it. See Matthew 12:33-37.