Deuteronomy 24:8

24:8 Take heed in the plague of leprosy, that you observe diligently, and do according to all that the priests the Levites shall teach you: as I commanded them, so you shall observe to do.
-World English Bible

Other Translation

24:8 Take heed in the plague of leprosy, that thou observe diligently, and do according to all that the priests the Levites shall teach you: as I commanded them, [so] ye shall observe to do.
-King James Version