Leviticus 13:5-8

5Then the priest shall look at him on the seventh day, and if in his eyes the infection has 1not changed and the infection has not spread on the skin, then the priest shall 2isolate him for seven more days. 6The priest shall then look at him again on the seventh day, and if the infected area has faded and the infection has not spread on the skin, then the priest shall pronounce him clean; it is only a rash. And he shall 3wash his clothes and be clean.

7“But if the rash spreads farther on the skin after he has shown himself to the priest for his cleansing, he shall appear again to the priest. 8And the priest shall look, and if the rash has spread on the skin, then the priest shall pronounce him unclean; it is leprosy.