Halakha Imamat 6:5: Sefer HaChinukh

From the laws of the commandment is that which they, may their memory be blessed, said that even though the fire descended from the Heavens in the days of Moshe, it is a commandment to bring [it] from the commoners, as it is stated (Leviticus 1:7), “And the sons of Aharon shall place fire, etc.” And (Mishnah Tamid 2) they would set up wood in the morning and make a large arrangement of wood at the top of the altar, as it is stated (Leviticus 6:5), “and the priest would burn wood each morning.” And besides the wood that was set up in the arrangement, it was a commandment upon the priest to bring up two blocks of wood, as it is stated, “and the priest would burn wood (etsim, which is plural)” — and the minimum of etsim is two. And so [too,] would they add two blocks of wood with the daily afternoon sacrifice; and two priests would bring them up, as it is stated, “and they shall set up” — but [for that] of the morning, [it was only] one priest.

And they would make three arrangements of fire on the altar every day. The first one was large, [and] upon it were the daily sacrifice and the other sacrifices offered; the second one on its side was smaller than it, [and] the fire was taken from it in the censer to burn the incense every day; and the third arrangement did not have anything upon it, so as to fulfill the commandment of the fire, as it is stated, “A perpetual fire shall burn, etc.” (Yoma 43b). And there are three passages about the topic, which instruct about these three arrangements, as we learned from the tradition. As they, may their memory be blessed, said (Yoma 45b), “‘Upon its burning’ (Leviticus 6:2), that is the large arrangement; ‘and the fire of the altar shall burn upon it’ (Leviticus 6:2), that is the second arrangement of the incense; ‘And the fire on the altar shall burn upon it’ (Leviticus 6:5), that is the third arrangement for the fulfillment of the fire.” And the rest of its details are elucidated in the fourth chapter of Yoma and the second of Tamid.