Halakhah sa Mga Awit 12:4: Chafetz Chaim, Mishneh Torah, Human Dispositions, Kitzur Shulchan Arukh & Sefer Chasidim

All this, only if one spoke demeaningly of his friend by chance. But if (G–d forbid) he is habituated to this sin, like those who customarily sit and say: "Thus and thus did Ploni (so and so) do," "Thus and thus did his fathers do," "This and this (demeaning thing) did I hear about him" — men such as these are called by Chazal "ba'alei (men of) lashon hara," and their punishment is far greater [than that of the former]. For in their perverseness of spirit and their malice of heart they transgress the Torah of the L–rd, and it becomes hefker to them, as explained above in the end of the introduction. And about them it is said in the tradition (Psalms 12:4): "Let the L–rd cut off all smooth-talking lips, the tongue that speaks haughtily."

Who is a sycophant? One who loads himself up with matters, and goes from this one to that one, saying to each, such did that man say, thus and such have I heard concerning that man, even though it be true, behold him, he destroys the universe. There is yet an extremely grosser iniquity, which, too, is included in this prohibitive commandment, and that is, the evil tongue, one who spreads scandal about his fellow even though he be telling truth. If he be lying, he is called a maligner who invents an evil name against his fellow. The owner of an evil tongue, behold him, he sits in company and relates, saying: thus and such did that certain party, thus and such were his parents, and thus and such I did hear about him and of course, he relates scandalous matters. Of him, the Verse says: "May the Lord cut off all flattering lips, the tongue that speaketh proud things" (Ps. 12.4).

The wise men said: "There are three transgresssions which call forth retribution from the man who perpetrates in this world, and disinherit him from a share in the world to come. They are: idolatry, adultery, and bloodshed; but the evil tongue outweighs them all" (Arakin, 16b). The wise men, moreover, said:³Arakin, 16b. G. "He who speaks with an evil tongue is like an atheist, for it is said: 'Who have said, Our tongues will we make mighty, our lips are with us, who is Lord over us'"? (Ps. 12.5.). And, again, the wise men said: "The evil tongue kills three persons, the one who speaks it, the one of whom it is spoken, and the one who receives it". In fact, the greatest harm comes to the one who receives the evil report.⁴Ibid.; Shabbat, 56. G.