Leviticus 6:9, 12-13

“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 until morning, and the fire of the altar shall be kept burning on it.

And the fire on the altar shall be kept burning on it; it shall not be put out. And the priest shall burn wood on it every morning, and lay the burnt offering in order on it; and he shall burn on it the fat of the peace offerings. A fire shall always be burning on the altar; it shall never go out.