Exodus 20:7
"You shall not take the name of the Lord your God in vain, for the Lord will not hold him guiltless who takes His name in vain."
Jesus said, "The good man brings good things out of the good stored up in his heart, and the evil man brings evil things out of the evil stored up in his heart. For out of the overflow of his heart his mouth speaks (Luke 6:45).
And He said, "Either make the tree good and its fruit good, or else make the tree bad and its fruit bad; for a tree is known by its fruit. Brood of vipers! How can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks. A good man out of the good treasure of his heart brings forth good things, and an evil man out of the evil treasure brings forth evil things. But I say to you that for every idle word men may speak, they will give account of it in the day of judgment. For by your words you will be justified, and by your words you will be condemned (Matthew 12:33-37, underlined for emphasis)
Colossians 3:17
"And whatever you do in word or deed, do all in the name of the Lord Jesus, giving thanks to God the Father through Him."
1 Peter 3:10
"For, whoever would love life and see good days must keep his tongue from evil and his lips from deceitful speech."
Ephesians 4:29
"Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen."
Philippians 4:8
"Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthymeditate on these things."
James 3:9-12
"With the tongue we praise our Lord and Father, and with it we curse men, who have been made in God's likeness. Out of the same mouth come praise and cursing. My brothers, this should not be. Can both fresh water and salt water flow from the same spring? My brothers, can a fig tree bear olives, or a grapevine bear figs? Neither can a salt spring produce fresh water."