Silence is the mark of those who are certain of the realities which have already come to be, and about which the Pen has already written. It is the key to every rest in this world and the next: it brings Allah's pleasure, a lightening of the reckoning and a protection from errors and mistakes. Allah has made it a veil for the ignorant and an adornment for the man of knowledge.
Through silence, passions can be set aside, and with it come self-discipline, the sweetness of worship, removal of hardheartedness, abstinence, virtuousness and resourcefulness. Therefore lock your tongue to speech which is not absolutely necessary, especially when you do not find anyone worth talking to; except, that is, when you are talking specifically about matters to do with Allah.
Rabi' ibn Khuthaym used to place a parchment before him, upon which he would write down everything he said during the day. In the evening he would call himself to account while he was still alive, seeing what he had said both for and against himself. Then he would say, 'Oh! The silent have indeed been saved!'
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 both to Allah, in Allah and for the sake of Allah, he would remove them from his mouth. Many of the Companions used to breathe like someone drowning, and speak like someone who was ill.
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 of his except the King of all, the All-compelling.