מדרש על במדבר 28:18

(Bamidbar 28:18) "On the first day it is a calling of holiness." Celebrate it with eating and drinking and with clean garments. "All work of labor you shall not do": We are hereby apprised that working is forbidden. And whence is it derived that the work that is needed for the preparation of food is permitted? From (Shemot 12:16) "Only (for) what is to be eaten by every person, that alone may be done for you." (Ibid. 19) "And you shall present a fire-offering, a burnt-offering to the L-rd": If one found bullocks but not rams, or rams but not lambs, I might think that he does not sacrifice any until he can sacrifice all. It is, therefore, written "And you shall present a fire-offering," implying even one. I might then think that even if all are found, (he may present only one). It is, therefore, (to negate this) written "two young bullocks, and one ram, etc."