Halakhah su Levitico 19:17

How great is the issur of lashon hara, which the Torah has forbidden even if true and in all modes. For not alone if he is careful to speak it only in private and to insist that it not be revealed to him [who is spoken about] is it forbidden, [for through this he also brings a curse upon himself, viz. (Devarim 27:24): "Cursed be he who smites his neighbor in secret"], but even if he knows that he would speak it even to his face, or actually speaks lashon hara to his face, even so it is forbidden and called "lashon hara." And in one respect, the issur is greater "to his face" than not to his face." For in his presence, aside from the issur of lashon hara, he [the speaker] clothes himself with the trait of brazenness and audacity, and arouses more strife thereby. And very often this leads also to the "whitening of (the other's) face (in shame)," as we have enlarged upon in the introduction concerning the negative commandment of (Vayikra 19:17): "Do not bear sin because of him."

After all, it is said in the Torah (Leviticus 19:17): "And you kept all my statutes and all my judgments and did them," and our sages said their remembrance of the blessing (Torah of the priests there): To give observance and doing to the laws as judgments. And the doing is known - that the laws will be done; And guarding - to beware of them, and not to seem to be inferior to the sentences, and the sentences - are the commandments whose taste is visible and the good of doing them in this world is known, such as robbery and bloodshed and honor of father and mother. And the laws - are commandments whose taste is not known. And our sages said their remembrance of the blessing (Shochar Tov Psalms IX): I have made laws for you and you have no permission to meditate on them, and the creation of man has been violated in them, and the nations of the world understand them, such as the prohibition of pork and meat in milk and decapitated cart

But if it appeared to them [see Rabbeinu Yonah 215, 218, and 220] that the sinner knew of the issur itself, and committed the sin intentionally — such as illicit relations, the eating of forbidden foods, or the like — the knowledge of this issur having spread in Israel, the following must be taken into consideration: "If he is "mediocre" in other things, usually guarding himself from sin, and in this sin having been seen to transgress only once and in secret, it is forbidden to reveal his sin to others, even not in his [the sinner's] presence, and he who does reveal it is guilty in doing so. For perhaps that sinner has repented of his evil way and his mind has been in turmoil over that sin, and he has been forgiven by the L–rd. For the root of repentance is bitterness of heart, and if he [the viewer] makes this sin public, he [the sinner] will be an object of scorn and mockery in men's eyes — after having repented of his evil and having been forgiven for his sin! Therefore, the fool, who mentions his sin, will himself be sinful and guilty. And it is not to be revealed even to the judges of the city, even if he has with him a second witness to substantiate his claim (for if not, then even without this [possibility of his having repented] it is forbidden to reveal it; for [since he is only a single witness], the judges are forbidden to believe his words and can only confirm him as "a speaker of lashon hara," as we shall explain below), and there can be no benefit in his doing so [i.e., in revealing the sin]. But he must reprove him in private for having rebelled against his G–d by sinning, and [he must] tell him to take care to "fence himself off" from the factors that brought him to it, so that he not come to sin again. And his reprover must take care to speak to him gently, so as not to shame him, as it is written (Vayikra 19:17): "Reprove shall you reprove your neighbor, but do not bear sin because of him [in reproving him harshly]." And all of this that we have written applies even if he is only a mediocre person in other respects; how much more so if he is a Torah scholar and a fearer of sin, who was suddenly overpowered by his evil inclination, in which instance it is a great sin to publicize his sin. And it is forbidden even to bethink himself of it, for [it is to be assumed that] he certainly repented and that though his evil inclination overpowered him once, his spirit is bitter unto him and his heart is extremely fearful within him over his guilt. As Chazal have said (Berachoth 19a): "If you have seen a Torah scholar who transgressed at night, do not think evil of him in the daytime, for he has certainly repented."