(I asked:) What is ḥifẓ al-lisān (guarding the tongue)? He said: It is silence (samt). (Adab, 94)
(The seven qualities that must be present in the murīd (aspirant, disciple)—which consist of the soundness of will, seeking causes for acts of obedience, knowing one’s nafs (the lower self), befriending those who know Allah, sincere tawba (repentance), lawful sustenance, and acquiring a righteous friend—are the nourishment of the will. The will attains moderation only through these. These seven qualities are supported by four others, which are the foundation and pillars of its structure. The first of these is hunger, the others are sleeplessness, samt (silence), and retreat (khalwa). These four qualities imprison the nafs and keep it under control. Binding the nafs with these qualities weakens its attributes and thereby improves its conduct. (Kūt, I, 94)
Samt (silence, speaking little, being quiet) is safety. The essential thing is safety. To remain silent where silence is forbidden brings regret. In determining the place to be silent in a particular ḥāl (spiritual state), one must consider the sharia (the sacred law), and the religious commands and prohibitions. To be silent at the right time is a characteristic of the people of Allah. Likewise, speaking at the right time is among the most noble qualities. I once heard Abū ʿAlī al-Daqqāq say: "Whoever remains silent where the truth is violated is a mute devil." Samt is among the etiquettes of presence. (Qushayrī, 62)
They say: The silence of the common people is with the tongue, the silence of the gnostics is with the qalb (the heart), and the silence of the lovers is possible by guarding the inspirations in their qalb.
They said to one of the Sufis: "Speak!" He replied, "I have no tongue to speak." They said, "Listen!" He replied, "I have no ear to listen." (Qushayrī, 64)
Samt is facilitated by retreat (uzla). Nevertheless, even one who retreats is not completely alone; he cannot avoid seeing the person who provides for his food, drink, and other needs. He should not speak with this person except out of necessity, for speech occupies the qalb. The qalb is greatly inclined toward speech. The qalb finds comfort in speaking, but engaging only in dhikr (remembrance of God) and contemplation is burdensome for it, and speech brings it relief. Samt, however, strengthens the intellect, teaches warāʿ (abstaining from doubtful things) and taqwa (God-consciousness). (Iḥyāʾ, III, 94)
The calamities of the tongue (āfāt al-lisān) are: error, lying, gossip, tale-bearing, hypocrisy, sowing discord, ugly speech, argumentation, self-justification, indulging in bāṭil (falsehood), enmity, unnecessary talk, distorting the truth, adding to or omitting from the truth, disturbing people, or attempting to stain the honor of the people.
These calamities of the tongue are many. They arise spontaneously and are not burdensome. The qalb finds them tasteful. Both human nature and the shayṭān contribute to this. Whoever indulges in these calamities of the tongue only restrains his tongue for a short time, letting it loose for what he loves and holding it back from what he dislikes. For this is among the difficulties of knowledge. Therefore, there is danger in indulging in speech, but safety in samt (silence). For this reason, the value of silence is great. Along with this value, samt also brings such good qualities as the gathering of himma (spiritual aspiration), the maintenance of dignity, setting aside affairs for reflection, dhikr, and worship, and being safe from having to account in the hereafter for what one spoke about in the world. (Iḥyāʾ, III, 138)