Musar על ערכין 30:7

And we learn also in Pirkei d'R. Eliezer: "Anyone who speaks lashon hara against his friend in secret has no cure, as it is written (Psalms 101:5): 'He who slanders his neighbor in secret, him will I cut off [forever].' And it is stated elsewhere (Devarim 27:24): 'Cursed be he who smites his neighbor in secret.' Come and see [what happened to] the serpent. Because he spoke lashon hara between the Holy One Blessed be He and Adam and his wife, the Holy One Blessed be He cursed him (Bereshith 3:14): 'And dust shall you eat all the days of your life.'" (That is, just as it is written there "all the days of your life," the intent being that he not be cured even in the days of the Messiah, as stated in Berachoth 12b: "the days of your life" — this world; "all the days of your life" — to include the days of the Messiah" — so, here, he [the speaker of lashon hara] has no cure forever.) And I have seen also in the holy books that if one speaks lashon hara, his sustenance diminishes, like that of a serpent [i.e., "And dust shall you eat, etc."]

(Ibid. 10): "And Aaron turned to Miriam, and, behold, she was leprous." For through the sin of lashon hara, plague-spots come, and his [the speaker's] punishment is to be a metzorah muchlat [a confirmed metzorah], as we find in the Gemara (Arachin 15b): "If one speaks lashon hara, he is afflicted with plague-spots, viz.: (Psalms 101:5): 'He who slanders his neighbor in secret, him atzmith,' and (Vayikra 25;30): 'latzmituth' which the Targum renders 'lachalutin'; [that is, that he be a metzora muchlat] concerning which we learned: 'The only difference between a quarantined leper [metzora musgar] and a confirmed [muchlat (similar to 'lachalutin')] leper is disheveling of the hair and rending of the clothes" [(these obtaining with the second, but not with the first)]. And the prayer of Moses availed her, but not entirely — only to change her from a confirmed leper to a quarantined leper.