Controlling The Tongue
The Messenger of Allah [s] says:
"Blessed is the man who speaks good and is triumphant; or keeps silent in the face of evil and is secure".
Among Allah's blessings upon man is that He made him a thoughtful and sane being and created a tongue for him. He made him able to utter sounds and clarify what he wants through the words which he speaks. He has only to speak to let people know what he wants.
Thus, we should thank Allah for the blessings which He bestowed upon us. We should use our speech in useful ways; not to speak but goodness. For example, if we are in a meeting or a gathering and want to speak with people, or any discussion comes up then we should first think what we want to say and choose which words to use. If we can offer useful counsel to people or offer advice, we should speak in such a way to make others want to listen. Hence your words will be acceptable to Allah and the people because your speech is beneficial in guiding towards goodness or reconciling people, or teaching useful knowledge, and will increase the love of people to each other. If we say a word of goodness we will get Allah's reward and the love and respect of the people and so we will be triumphant. As our glorious Prophet Muhammad [s] says: If man is not able to say something useful, he should keep silent from bad words and his silence will keep him far from Allah's wrath and from the harm which might befall him as a result of saying bad words. Whoever does evil deeds to people, people will surely confront him with evil too. And certainly, if you speak bad words it may cause you problems and harm and make you regret and wish you had kept silent and had not spoken.
Consequently, our Holy Prophet Muhammad [s] educates us with good manners saying: Either you speak a useful and good word, or be silent which is better for you than speaking evil words.
1. Among the best characteristics of a Muslim is to speak only the words of goodness and reconciliation.
2. It is better to remain silent if you cannot speak the word of goodness.
3. Whoever does not keep a check on his tongue will regret it.
For those who do good is good (reward) and even more than that.
 Tabrasi, Mashkat al-Anwar, p. 175, 2nd Edition.