NUM145 … lashon hara [Lit., "evil tongue," i.e., communicating something bad about another person] brings a person to speak falsely against Hashem, [Yeshayahu 32:6] as the pasuk says (Tehillim 73:9), "They have set their mouth against Heaven, even though their tongue goes up on the earth." Among all the transgressions none come close to the punishment incurred by one who tosses words [abusively against Hashem]. Our Sages said (Arachin 15a) that our forefathers tested [ Hashem] ten times [in the wilderness], but their decree was only sealed over the sin of lashon hara, as the pesukim say [this verse], "Surely, as you have spoken in My ears, I will do to you," and (Devarim 1:34), "Hashem heard the sound of your words, and became angry and made an oath, saying…" [The Jewish people were punished by not being able to enter Eretz Israel after maligning the land and Hashem.] The pasuk also says (Malachi 2:17), "You have wearied Hashem with your words."