Our words should please God. It's in the Bible, Psalm 19:14, NIV. "May the words of my mouth and the meditation of my heart be pleasing in Your sight, O Lord, my Rock and my Redeemer."
Words are so powerful that silence is sometimes the best action. It's in the Bible, Proverbs 13:3, NIV. "He who guards his lips guards his life, but he who speaks rashly will come to ruin."