The term לשון הרע is well known as a basic rule in guiding our speech. We are to “guard our tongues” and take great care not to speak badly about people.
It is interesting to note that the words ״לשון הרע״ are not found anywhere in Tanach. Nevertheless, there is both a positive and negative commandment connected with forbidden speech.
The negative commandment is found in פרשת קדושים, where it says, לא תלך רכיל בעמך, that we are not to around as peddlers of gossip. And the positive commandment according to Rabbeinu Bechaye is learned from כי תצא where it says, זכור את אשר עשה ה׳ אלוקיך למרים, that we are to remember what Hashem did to Miriam. We are to actively take care not to speak לשון הרע as Miriam did. Needless to say how damaging negative speech can be. But we are also to be aware that such speech violates both a positive and negative Torah commandment.