Leviticus 13:5-8

5The priest shall look at him on the seventh day, and if in his eyes the infection 1has not changed and the infection has not spread on the skin, then the priest shall 2isolate him for seven more days. 6The priest shall look at him again on the seventh day, and if the infection has faded and the mark has not spread on the skin, then the priest shall pronounce him clean; it is only a scab. And he shall 3wash 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 cleansing, he shall appear again to the priest. 8The priest shall look, and if the scab has spread on the skin, then the priest shall pronounce him unclean; it is leprosy.