Leviticus 6:11

And put on other garments - The priests approached the altar in their holiest garments; when carrying the ashes, etc., from the altar, they put on other garments, the holy garments being only used in the holy place.

Clean place - A place where no dead carcasses, dung, or filth of any kind was laid; for the ashes were holy, as being the remains of the offerings made by fire unto the Lord.