Salaam and Greetings of Peace:
One of the Companions of the Messenger of Allah used to put pebbles in his mouth. When he wanted to say something he knew was to Allah, in Allah, and for the sake of Allah, he would remove them from his mouth.
People’s destruction or salvation lies in speech and silence. Good fortune belongs to those who are given knowledge of what is incorrect and correct in speech, and the science of silence and its advantages, for it is one of the qualities of the prophets and one of the distinguishing marks of the select. Whoever knows the value of speech is an expert in the company of silence: once a person has been exposed to the subtleties of silence, and has been entrusted with its treasures, then both his speech and silence are worship. No one is privy to this worship except the King of all, the All-Compelling.
From Lantern of the Path by Imam Jaffar Al-Sadiq