Leviticus 13:5-8

5The priest shall examine it on the seventh day, and if in his estimation the infection has not changed and has not spread on the skin, then the priest shall isolate him for seven more days.

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.