Musar על ערכין 29:6

They taught (Erchin 15b): "What is [the dust of] slander? [Answer:] For instance to say 'where else should there be fire if not in the house of so-and-so?' (implying that there is always meat and fish there)". Or to praise a person before one who hates him. Likewise for all similar cases, even though they may appear like insignificant words, far removed from tale-bearing, behold, in truth, they are of the "dust" of slander.

(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.