(1) If one saw a person harming a friend, whether robbing them, oppressing them, or causing them damage— whether the one robbed or caused damage knew of it or not — or shaming them or aggrieving them, or wronging them with words, and it became known to one clearly that the theft was not returned and the damage was not redressed and they were not sought out for forgiveness for the transgression, then even if one saw this thing alone, one can relate it to others in order to help them who were wronged and to condemn these evil deeds before people; but one must take care that one not fall short with regard to seven criteria which we shall now explain:

(1) That one see the thing oneself and not hear of it from others, unless it become clear to one afterwards that the thing is true.

(2) That one take great care not to immediately determine the thing to be theft, or oppression, or damage, and the like, but rather examine the essence of the matter well, determining whether it is theft of damage according to the law.

(3) That one reprove the sinner first, gently — perhaps this will help so that they rectify their ways. And if they do not listen, then one should apprise the public of this person's guilt — how they deliberately harmed their friend.

(And if one knows that the reproof will not be accepted — this will be explained below, God willing, in section 7.)

(4) That one should not exaggerate the wrong beyond what it is.

(5) That one's intention should be for good, and not (as is explained below in section 4), God forbid, to benefit oneself from this taint that one ascribes to a friend, and not out of hatred that one bears from before.

(6) If one can bring about the desired good in another way, without needing to tell of the matter that is evil speech about a person, then, in all instances, it is forbidden to tell.

(7) That one should not cause through the telling more damage to the one spoken about than is appropriate, and than that would come out if this matter was adjudicated in court (The rationale for this is to be found below in the laws of rechiluth, Principle IX, where it properly belongs.)

. . . 

(1) The fifth criterion that we wrote of above, namely, that one's intention be for good, is as we shall explain. That is, it is not necessary that the people to whom one tells [the story] can help the one who was robbed, or oppressed, or damaged, or shamed, [if so] then certainly it is correct to do this [i.e., to expose the perpetrator]. But even if this benefit cannot result through one's telling, and one only intends that people will distance themselves from the way of wickedness when they hear of it—since people condemn those who do wrong—and perhaps that the same one [who is spoken of] will repent of evil ways and improve their actions—because of people's condemnations—this too is not in the category of "lashon ha-ra" and can be considered a good intention, since in any case, one is not intending to benefit from the taint ascribed to a friend but only to be zealous for the truth, that perhaps some future benefit will result.

There was a certain rabbinical student who had a bad reputation.

Rav Yehuda said: What should be done? Should I excommunicate him? But the Sages need him! Should I not excommunicate him? But this would be to desecrate the Name of Heaven!

He said to Rabba bar bar Ḥana: Have you heard anything with regard to this issue?

He said to him: Rabbi Yoḥanan said as follows: What is the meaning of that which is written: “For the priest’s lips should keep knowledge, and they should seek Torah at his mouth; for he is a messenger of the Lord of hosts” (Malachi 2:7)? This verse teaches: If the teacher is similar to a messenger of the Lord, then seek Torah from his mouth, but if he is not, then do not seek Torah from his mouth.

Rav Yehuda excommunicated him.

In the end, Rav Yehuda took ill. The Sages came to inquire about his well-being, and he [the one who had been excommunicated] came together with them. When Rav Yehuda saw him, he laughed.

He [the excommunicated scholar] said to him: Was it not enough that you excommunicated me, you even laugh at me?

Rav Yehuda said to him: I was not laughing at you; rather, as I got to the next world, I am happy that I did not flatter even such a man as you.

Rav Yehuda died.

He [the excommunicated scholar] came to the Beit Midrash and said to them [the Sages]: Release me!

The Rabbis said to him: There is no man here as important as Rav Yehuda who could release you, but go before Rabbi Yehuda Nesiah so that he can release you.

He went before him.

He [Rabbi Yehuda Nesiah] said to Rabbi Ami: Go, examine his case. If he ought to be released, release him!

Rabbi Ami examined his case and decided to release him.

Rabbi Shmuel bar Nahmani stood up on his feet and said: With regard to the maidservant of Rabbi's household, the Sages did not make light of the excommunication she imposed for three years; with our colleague Yehuda, how much the more so!

Rabbi Zera said: What does this mean that this aged man [Rabbi Shmuel bar Naḥmani] who has not come to the Beit Midrash for how many years now appears? Conclude from this that he ought not be released!

He was not released. He left, crying. A wasp came and stung him on his member and he died.

They brought him to the burial cave of the righteous and he was not accepted. They brought him to the cave of the judges and he was accepted.

What is the reason?

Because he acted in accordance with Rabbi Illai, for it is taught: Rabbi Illai says: If a person sees that his impulse overcomes him, let him go to a place he is not known, wear black clothes and wrap himself in black, and let him do what his heart desires but let him not profane the name of Heaven in public.

(1) All commandments of the Torah, whether they be mandatory or prohibitive, if a person violates any one of them, either deliberately or erroneously, in undertaking to repent and to turn away from sin, one is obliged to confess before God. . .

And so too, one who injures a friend or causes damages in money matters, even though one makes restitution of what one owes, one finds no atonement until one makes verbal confession and repents by obligating oneself never to repeat this again, even as it is said: "from any of a person's sins."

Mishneh Torah 2:5

It is highly praiseworthy for a penitent to confess publicly, letting the public know one's iniquities, and exposing sins between oneself and one's neighbor to others, saying to them: "Truly, I have sinned against So-and-So, doing thus and such, but, behold me this day, I repent and am remorseful". But anyone who is arrogant and does not expose but covers up sins, this penitence is not complete, as it is said: "One who covers up sins shall not prosper" (Prov. 28.13). But to what does this refer? Only to sins between one person and another, but with sins between a person and God, the penitent need not make them public, on the contrary it would be impudent of him to expose them.