(17) Shimon, his son, says, "All my days I grew up among the Sages, and I did not find anything good for the body except silence. And the exposition [of Torah] is not what is essential, but the action. And whoever increases words brings sin."

(5) There are times when silence is good, as when divine justice strikes against a man, as in the case of Aaron, as it is written, "And Aaron held his peace" (Lev. 10:3). If a person hears people reviling him, he should be silent. And this is a great quality, to be silent in the face of one's revilers.

And one should also accustom himself to be silent in the synagogue, for this is modesty and it requires great alertness properly to direct his heart in prayer.

And if one is sitting among the wise he should be silent and listen to their words, for when he is silent, he hears what he does not know, but when he speaks he does not add anything to his knowledge. However, if he is doubtful as to the meaning of the words of the wise he should ask them, for to be silent in such a case is very bad: King Solomon said, "A time to keep silence, and a time to speak" (Eccl. 3:7) — there are times when speaking is good and there are times when silence is good.

And the wise man said, "When you do not find a man who can teach you morality, then cleave to silence lest you speak folly." And since the tongue is very facile, one must take care to make it heavy, to guard it so that it does not speak. An abundance of words is like a heavy burden, and the weight of many words is more difficult to bear than the weight of much silence.

And if a man hears his neighbor speaking he should be silent until he finishes, "He that giveth answer before he heareth, it is folly and confusion unto him" (Prov. 18:13).

(6) He who is accustomed to be silent, is saved from many transgressions : from flattery, from mockery, from gossip, from lies, and blasphemies. For when a man shames and reviles him, if he answers him, then the offender will double his reviling and his insults. And thus said the wise man, "I hear a bad word, but I am silent." And they said to him, "Why?" And he said to them, "If I respond or answer my revilers, I fear that I will hear other insults much worse than the first."

And he said, "Where a fool takes issue with a wise man, and the wise man is silent, this in itself is a great answer to the fool." And he said, "A fool has greater anguish in the silence of the wise man, than if the wise man would respond to him." And on this it is said, "Answer not a fool according to his folly, lest thou also be like unto him" (Prov. 26:4).

(7) Then too, if a person is silent, others can reveal secrets to him, for inasmuch as he is not accustomed to speak much he will not reveal the secret.

(8) But there are times when silence can be evil, as it is written, "Answer a fool according to his folly, lest he be wise in his own eyes" (Prov. 26:5). With respect to words of the Torah, if a person sees that the fools are scorning the words of the wise, he should answer in order to turn them back from their errors so that they do not imagine themselves wise in their eyes. If a man sees another man committing a transgression, he should protest and reprove him.

Moreover, it is not his habit to indulge in gossip, and concerning this it is said, "Death and life are in the power of the tongue" (Prov. 18:21), for a man can do more harm with his tongue than he can with a sword. For a man can stand here and yet betray his companion, who is a long distance from him, and cause his death (by his word), while the sword can only slay someone who is near it. Therefore man was created with two eyes, two ears, two nostrils and one mouth to say to him that he ought to speak less.

Maimonides, Hilchot De’ot 7:3

Negative speech is a transgression equivalent to murder because it kills three people, not one: the one who said it, the one who heard it, and the one about whom it was said.

(14) The general rule here is this : When a man makes a door for the entrance to his house, there is a time to open it and a time to close it. So should he close the doors of his mouth, for there are actually two doors, the lips and the teeth. And be very careful as to when you open your mouth, and guard your tongue as you would silver and gold and pearls in your room and in your jewel case, and make a lock for the lock. Observe how the Sages of old guarded themselves from idle talk all their days.