Rashi on Deuteronomy 24:9/רש"י על דברים כ״ד:ט׳

1זכור את אשר עשה ה' אלהיך למרים REMEMBER WHAT THE LORD THY GOD DID UNTO MIRIAM — if you wish to guard yourself against being stricken with leprosy, do not speak slander! Remember what was done unto Miriam who spoke slander against her brother and was stricken with a leprous plague! (cf. Sifrei Devarim 275:1).