NUM226 "That he not be like Korach and his assembly" [this verse]. Our Sages, z"l, said (Sanhedrin 110a), "Whoever supports controversy is violating a negative commandment, as the pasuk says, "That he not be like Korach and his assembly." It is [even] permissible to speak lashon hara about one who is the source of dissension [See Sefer Chafetz Chaim (Hilchos Lashon Hara 8:8) for caveats regarding this leniency] as the pasuk says (I Melachim 1:26), "But me -- I, your servant--and Zadok the Kohen, Benayahu son of Yehoyadah, and your servant Shlomo, he did not invite." [Nosson HaNavi told David HaMelech this denigrating information about David's son, Adoniyahu, who was attempting to usurp the throne.]