He prohibited us from cutting off signs of impurity or burning them until their appearance changes. And that is His saying, "Take heed of the plague of tsaraat" (Deuteronomy 24:8). And the language of the Sifrei (Sifrei Devarim 274:1) is, "'Take heed' - is with a negative commandment." And the language of the Mishnah (Mishnah Negaim 7:4) is, "One who plucks out signs of impurity or burns healthy flesh transgresses a negative commandment." And he is lashed, as we have explained (Commentary on the Mishnah, Negaim). (See Parashat Ki Tetzei; Mishneh Torah, Defilement by Leprosy 1.)