Leviticus 6:9-10

9“Command Aaron and his sons, saying, ‘This is the law of the burnt offering: the burnt offering shall remain on the hearth that is on the altar all night until morning and the fire is to be kept burning on the altar.

10The priest is to put on his linen robe, with his linen undergarments next to his body. Then he shall take up the ashes of the burnt offering which the fire has consumed on the altar and put them beside the altar.