Charles Ellicott Commentary Leviticus 6:9

"Command 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." — Leviticus 6:9 (ASV)

It is the burnt offering, because of the burning upon the altar. — Better, This, the burnt offering, shall be upon the fire on the altar. That is, the continued burnt offering, with which the sacrifices here enumerated begin, is to remain burning upon the altar from the evening until the morning. (Numbers 28:1–8).

Shall be burning in it. — Better, shall burn by it. That is, it shall be fed and kept up by it. According to the practice that was customary during the second Temple, the fat pieces of the burnt offering began to be burned at midnight, thus feeding the fire until the break of day.