Leviticus 13:1-3

And Jehovah spake unto Moses and unto Aaron, saying, When a man shall have in the skin of his flesh a rising, or a scab, or a bright spot, and it become in the skin of his flesh the plague of leprosy, then he shall be brought unto Aaron the priest, or unto one of his sons the priests: and the priest shall look on the plague in the skin of the flesh: and if the hair in the plague be turned white, and the appearance of the plague be deeper than the skin of his flesh, it is the plague of leprosy; and the priest shall look on him, and pronounce him unclean.