Halakhah zu Wajikra 1:7

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.