Assalam alaikum,
The Sunnah of the Prophet Muhammad, peace and blessings be upon him, regarding speech is based on a Hadith related by Abu Hurairah, may Allah be pleased with him, in which the Prophet, peace be upon him, was reported to have said:--
"WHOEVER BELIEVES IN ALLAH AND THE LAST DAY, LET HIM
SAY WHAT IS GOOD OR REMAIN SILENT." [Sahih Bukhari].
The default of one's speech is that one remains silent and does not speak unless one is sure that his speech will be good. if one is unsure if it will be good or bad then one remains silent.
So, the Sunnah is that one remains silent until one is sure.
Some of the sins related to one's tongue, which we should avoid, include:--
Ghiba (backbiting), Namima (gossiping), Suma (showing off with speech), Kazib (lying) and Iftikhar (boasting to others, making claims). Note this well.
Subject: Observe This Sunnah. 
July 16th 2014, 6:43 pm