Albert Barnes Commentary Leviticus 6:10

"And 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." — Leviticus 6:10 (ASV)

Ashes ... with the burnt-offering - Rather, the ashes to which the fire has consumed the burnt-offering.