Moussar sur Les Psaumes 5:10

Evil speech is the head root sprouting poison (alluding to Deuteronomy 29:17), for its severity corresponds to that of idolatry, sexual immorality, and murder [put together] (Arkahin 15b). And King David, peace be upon him, has already expunged it, as it is written: May the Lord expunge all flattering lips, every tongue that speaks arrogance (Psalms 12:4). And evil speech is when one speaks disparagingly about his fellow. If it is something that has nothing to it, it is also called putting out a bad name. But if it is true, it is called evil speech – anything that was not known and this one reveals it. A talebearer reveals secrets (alluding to Proverbs 11:13), as he carries things to and fro and says, “X did this to you,” or “said this and that about you.” Their tongue is a sharpened arrow (alluding to Jeremiah 9:7); their throat is an open grave (alluding to Psalms 5:10). However, if he sees that damage will come to his fellow, he is obligated to reveal it to him so that he can be on guard. About this is it stated: You are not to traffic in slander among your kinspeople, you are not to stand by the blood of your neighbor; I am the Lord (Leviticus 19:16).