On the authority of Abu Huraira who said that the Messenger of Allah (peace be upon him) said, "A good word is a charitable act." [Bukhari, Muslim]
In this hadith one finds an excellent but easy means by which to spread happiness and perform a charitable act. Very few humans are without the physical and mental means to perform this act that is beloved to Allah and that should be performed as an expression of gratitude to Allah.
The expression, "a good word," includes many things. Sindi defines it as "any word by which Allah is remembered or any word which benefits any of Allah's creation."
The words used in making remembrance of Allah (dhikr) are good words. Verbally ordering what is good and eradicating what is evil are considered good words. Advising one's brother forms part of this concept. Speaking to the people in a way that makes them pleased and happy is also a charitable act for the person.
An advanced form of speech is one of the aspects that distinguish humans from the animal world. One should use the very important power of speech for what is good. A believer should either speak what is good or remain silent. To use one's tongue in any other way is a gross misuse of this great blessing of speech that Allah has bestowed upon humans.
"Commentary on the Forty Hadith of al-Nawawi" - Jamaal al-Din M. Zarabozo, p. 1002