One of the morals taken into account and given importance by Islam is as minor as excellence of meeting with a smiling countenance and politeness in speech. Provided we have faith in our hearts, we are told that if we lack the means of providing a date or even half a date to the needy we can truly make an equal difference and manage to have the same benefit in terms of rewards from Allah (SWT) by consoling a fellow human being through our compassionate tone of voice. It is also said that a sharp tongue can cut your own throat. I believe it doesn’t take much of an effort to beautify our speech with kind words, as words like sword, have a rather sharp and long lasting effect. This matter could be signified and is evidently related to a student-teacher relationship, a parent advising his/her child, or generally when we interact with other people be it for work or casually between friends.
Abu Hurairah (May Allah be pleased with him) reported: The Prophet (PBUH) said, "It is also charity to utter a good word.'' [Al-Bukhari and Muslim].
Therefore we can clearly see that in Islam donating money to a charity organization or to the poor isn’t the only form of charity but luckily for the believers talking to anybody in a decent manner is taken in the same context.
On another occasion Abu Dharr (May Allah be pleased with him) reported: Messenger of Allah (PBUH) said, "Do not disdain a good deed, (no matter how small it may seem) even if it is your meeting with your (Muslim) brother with a cheerful face.'' [Muslim].
Howsoever it may appear quite insignificant to some people, even meeting others cheerfully is one of the Islamic virtue and every good deed which is approved by the Shari’ah is also rewarded by the Shari’ah.
This is also supported by verses in the Quran in which Allah, the Exalted, says:
"And lower your wings for the believers (be courteous to the fellow-believers).'' (15:88)
"And had you been severe and harsh-hearted, they would have broken away from about you.'' (3:159)
Some of the sins related to one’s tongue are ghiba: (Backbiting), namima: (Gossiping), suma (showing off (riya) with speech), iftikhar (boasting to others, making claims), kadhib (lying) and khawd fi al-batil (mentioning the useless or immoral).
Abu Hurayr( May Allah be pleased with Him) said, "Truly a man utters words to which he attaches no importance, and by them he falls into the Fire of Jahannam, and truly a man utters words to which he attaches no importance, and by them Allah raises him into the Garden."
Surely the Hadith, Sunnah and the Quran clearly outlines and expresses the importance of learning how to control one’s speech which could possibly be very difficult to implement because of how often we speak.