Leviticus 6:9-10

9Command Aaron and his sons, saying, This is the law of the burnt offering: the burnt offering shall be on the hearth upon the altar all night unto the morning; and the fire of the altar shall be kept burning thereon.

10And the priest shall put on his linen garment, and his linen breeches shall he put upon his flesh; and he shall take up the ashes whereto the fire hath consumed the burnt offering on the altar, and he shall put them beside the altar.