Negative commandment · Lo Ta’aseh #81 of 613
Not to extinguish the fire of the altar
שלא לכבות אש המזבח
The verse · Vayikra 6:6
אֵשׁ תָּמִיד תּוּקַד עַל־הַמִּזְבֵּחַ לֹא תִכְבֶּה
“The fire shall ever be burning upon the altar; it shall never go out.”
The Rambam’s words
Not to extinguish the fire of the altar, as [Leviticus 6:6] states: "Burn a continuous fire on the altar. Do not extinguish it."
שלא לכבות אש המזבח, שנאמר "אש, תמיד תוקד על המזבח--לא תכבה" (ויקרא ו,ו).
Who & when
“And it is practiced at the time of the [Temple] by males and females — even Israelites.”
Where in the Mishneh Torah
Hilchot Daily Offerings and Additional Offerings הלכות תמידים ומוספין