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 unto the morning; and the fire of the altar shall be kept burning thereon.

And the fire upon the altar shall be kept burning thereon, it shall not go out; and the priest shall burn wood on it every morning: and he shall lay the burnt-offering in order upon it, and shall burn thereon the fat of the peace-offerings. Fire shall be kept burning upon the altar continually; it shall not go out.