Commentaire sur Le Lévitique 6:6

אש תמיד — The redundant word תמיד (because it could have written לא תכבה המזבח ‎אש תוקד על‎ ; for this, too, would imply that it must be continually burning since it states that it must never go out) intimates: The fire about the use of which the expression תמיד is used, viz., that by which the lamps of the Candelabrum were kindled, with reference to which it is said, (Exodus 27:20) “to light the lamps continually (תמיד), this, too) should be ignited from the fire on the outer altar Yoma 45b).

That too is kindled from the outer altar. You might ask: Above, Rashi explains: “[The Torah] here includes many kindlings and all of them are expounded in Maseches Yoma,” and he brings the verse “a continual fire” there as well! [Why, then, is it available for a drashah here?] The answer is: This is what Rashi means above: [The Torah] here includes many kindlings, but why are they needed? It is understandable [that the Torah mentions] “a continual fire” — I need to expound from it “a fire of which it is said, ‘continual,’ [etc.]” However, why do I need the rest? With regard to this Rashi explains: “All of them are expounded [in Maseches Yomo].”

אש תמיד, “a perpetual fire;” it will be kept burning even on the Sabbath, even if for some reason it became ritually impure.