Leviticus 6:9, 12-13

“Give Aaron and his sons the following instructions regarding the burnt offering. The burnt offering must be left on top of the altar until the next morning, and the fire on the altar must be kept burning all night.

Meanwhile, the fire on the altar must be kept burning; it must never go out. Each morning the priest will add fresh wood to the fire and arrange the burnt offering on it. He will then burn the fat of the peace offerings on it. Remember, the fire must be kept burning on the altar at all times. It must never go out.