Leviticus 22:1-3

And the Lord said to Moses, Give orders to Aaron and to his sons to keep themselves separate from the holy things of the children of Israel which they give to me, and not to make my holy name common: I am the Lord, Say to them, If any man of all your seed through all your generations, being unclean, comes near the holy things which the children of Israel make holy to the Lord, he will be cut off from before me: I am the Lord.