Leviticus 13:6-8

6The priest shall examine him again on the seventh day, and if the infection has a more normal color and the spot has not spread on the skin, the priest shall pronounce him clean; it is only a scab; and he shall wash his clothes and be clean.

7“But if the scab spreads farther on the skin after he has shown himself to the priest for his [ceremonial] cleansing, he shall show himself to the priest again.

8The priest shall look, and if the scab has spread on the skin, then he shall pronounce him unclean; it is leprosy.