The believers are encouraged to be thoughtful and to speak only with discretion and forethought as to the likely effects of the words they utter. For those who do so, the following Hadith promises a great spiritual reward:
"When a servant of God says that which is clear and correct (i.e. having given thought to whether it is beneficial or not), through (his words) he is distanced from the Fire by a distance greater than that what is between sunrise and sunset." [Riyad As-Saleheen]
When quoting this Hadith, Al-Nawawi makes the following observation: "although talk that is not for the sake of a benefit is generally frowned upon, conversation with one's guests, discussion in pursuit of knowledge and remembering the virtues of upright and pious are not discouraged."
"Freedom of Expression in Islam" - Mohammad Hashim Kamali, pp. 129, 130