Midrasch zu Wajikra 13:28

3) (Vayikra 13:24) "a burn by fire": I might think that only a "rebellious" (i.e., unhealed) burn were intended. It is, therefore, written "and the healthy flesh of the burn." (If the latter alone were written,) I might think that it must form a scab; it is, therefore, written "a burn by fire." How is this to be reconciled? It healed and did not heal (i.e., it formed a peel and not a scab) And thus is it written below (Vayikra 13:28) "it is the peel of the burn" — until it forms a membrane, like a garlic peel.