leviticus 6:9 Command Aaron and his sons, saying, This is the law of the burnt offering: It is the burnt offering, because of the burning upon the altar all night unto the morning, and the fire of the altar shall be burning in it. - Free Bible Online

      9. Command Aaron and his sons, saying, This . . . law of the burnt offering--In this passage Moses received instructions to be delivered to the priests respecting their official duties, and first the burnt offering--Hebrew, "a sacrifice, which went up in smoke." The daily service consisted of two lambs, one offered in the morning at sunrise, the other in the evening, when the day began to decline. Both of them were consumed on the altar by means of a slow fire, before which the pieces of the sacrifice were so placed that they fed it all night. At all events, the observance of this daily sacrifice on the altar of burnt offering was a daily expression of national repentance and faith. The fire that consumed these sacrifices had been kindled from heaven at the consecration of the tabernacle [Le 9:24], and to keep it from being extinguished and the sacrifices from being burned with common fire, strict injunctions are here given respecting not only the removal of the ashes [Le 6:10, 11], but the approaching near to the fireplace in garments that were not officially "holy."

JFB.