Leviticus 13:6-8

6Then the priest shall examine him again on the seventh day; and indeed if the sore has faded, and the sore has not spread on the skin, then the priest shall pronounce him clean; it is only a scab, and he shall wash his clothes and be clean.

7But if the scab should at all spread over the skin, after he has been seen by the priest for his cleansing, he shall be seen by the priest again.

8And if the priest sees that the scab has indeed spread on the skin, then the priest shall pronounce him unclean. It is leprosy.