Musar על במדבר 12:9

And they also expounded (in Vayikra Rabbah 16) the verse (Koheleth 5:5): "Do not allow your mouth to cause sin to your flesh" — do not speak lashon hara with your mouth to punish all of your flesh with this sin. The Rabbis applied this verse to Miriam: "Do not allow your mouth" — you, Miriam, as it is written (Numbers 12:10): "And, behold, Miriam was leprous, [white] as snow." (Koheleth, Ibid.): "that it was an error" — as it is written (Numbers 12:11): "wherein we [(Aaron and Miriam)] have erred and wherein we have sinned." (Koheleth, Ibid.): "Why should G-d be angry at your voice?" — at the lashon hara you have spoken against Moses, as it is written (Numbers 12:9): "and the anger of the L-rd burned against them, and He departed." (Koheleth, Ibid.): "and [He shall] destroy the work of your hands." R. Yochanan said: "With her mouth she sinned, and all her limbs were smitten, as it is written (Numbers 12:10): 'And the cloud departed from the tent, and, behold, Miriam was leprous, [white] as snow.' This is the intent of: "Do not allow your mouth to cause sin to [destroy] your flesh" … (Mishlei 21:33): 'He who guards his mouth and his tongue guards his soul from troubles.'"