In Usul al-Kafi, it is narrated, "Preserve your tongue from idle talk, because the majority of the sins committed by the son of Adam is due to the tongue only. No other part of the body commits more sins than the tongue." And in Nahjul Balagha: "When Allah wishes to bless His servant, then He helps him in controlling his tongue. Instead of finding faults in others, Allah keeps him busy in looking at his own defects. Those who speak less, their intelligence is complete and their hearts are pure. Those who speak more, their intelligence is incomplete and their hearts are hard. A God-fearing man's tongue should be behind his heart. First, he should think, then he should speak justly. Otherwise he should keep quiet. A hypocrite acts just the opposite of this. He keeps talking rubbish. He is not worried about what he is saying."
All of us should worry about words and take care in what we say.
Advice for avoiding sins of the tongue includes the following ten tips:
1. Stay out of conversations that do not concern you.
2. Avoid arguing, even if you are in the right.
3. Do not say anything about someone else unless it is true, good, and useful. Say something bad about someone only if it is truly necessary to avoid a greater harm, such as to protect someone from becoming a victim of a crime.
4. Think before you speak; like feathers from a pillow blown away by the wind, words cannot be taken back, and their effects cannot be undone. You cannot control how others will respond to your careless words or what their effects will be. All you can do is control what comes out of your mouth to begin with.
5. Do not use language to try to impress people or sound cool. Use normal, proper speech and avoid slang, excessive eloquence, and false accents.
6. Do not swear or use obscene language. One narration from the Holy Prophet (peace be upon him and his progeny) states, "Heaven is forbidden to whoever is used to swearing/cussing. He cannot enter it." It also destroys your respect in the eyes of others.
7. Speak the truth, even if it is against you. Let your word be reliable.
8. Avoid sexualized speech or dirty talk. Do not degrade the opposite sex or your own through your words, ever, and do not cheapen marital relations with your tongue.
9. Do not break confidences with your tongue. You should avoid saying anything to anyone that you would not want revealed to all, unless truly necessary. Likewise, you should never mention about someone else what they would wish to be kept private. For example, men and women should not talk about their quarrels or relations with their spouses to others, children should not carelessly reveal the bad habits of their parents, parents should not embarrass their children by talking about their past mistakes, etc.
10. Do not listen to any of the negative speech above, even in poetry or music – do not lend your ear to arguments, backbiting, bad-mouthing, cussing, obscenity, lies, etc., as even choosing to listen to such speech is sinful, it promotes such behavior from your own tongue, and it hardens your heart. Actively avoid such speech, and prevent or stop it when possible.
People who are careful about their words enjoy many benefits. Those known for gentle, kind, good speech and avoiding unnecessary and negative talk earn respect and trust from other people. Friends will feel safe with them, and people will be more at ease to do business with them. They will enjoy a good reputation. They hear more good things and thus learn more and are more likely to have an expansive and enlightened heart. There is no down side to guarding your tongue, and everyone can do it with practice and effort. No other part of the body commits more sins than the tongue, but if we are diligent, we can make ourselves the exceptions.