Do not speak without thinking. You should only speak once you have pondered over what you wish to say and you are convinced that it will not be badly received. It is a sin to address a person or speak of him in the following terms: “he has no Imaan”, “may Allah’s punishment, curse, or anger descend on a certain person”, “may he enter hell”, etc. It is a sin to speak in this manner irrespective of whether one is addressing a human or an animal. If the person who has been addressed in this manner does not deserve such remarks, all these curses will actually descend on the person who uttered them. If anyone addresses you in this useless manner, you have the right to reply in the same way. However, you cannot exceed what that person says. If you exceed, you will be committing a sin. Do not be two-faced whereby you “play according to the tune” of one person when you are in his company, and according to the “tune” of another person when in the latter’s company. Don’t ever back-bite nor should you listen to such back-biting and tale-bearing. Never ever speak a lie. Do not praise a person directly nor should you exaggerate in praising him in his absence. Don’t ever involve yourself in ghebah. Ghîbah means speaking in the absence of a person in such a way that if he were to hear it, he would be grieved. This is irrespective of whether what you say is the truth or not. If what you say is false, it is regarded as slander or defamation. This is even more sinful.
