Sefer HaChinuch ספר החינוך

To not eat higher-level consecrated foods (kodshei kodashim) outside of the [Temple] yard: To not eat — and even priests — from the meat of the sin-offering, and the guilt-offering outside of the “curtains.” And the masters of the tradition explained that this prohibition is included in “You may not eat in your gates, etc. your cattle and your flocks” (Deuteronomy 12:17). As so did they, may their memory be blessed, say (Makkot 17a), “The verse only comes with regard to one who eats a sin-offering or a guilt-offering[...] outside the curtains, [to teach that he is transgressing a negative commandment].” And so too, one who eats lower-level consecrated foods (kodashim kalim) outside of the wall [of Jerusalem] is included in this prohibition, like the Gemara comes to teach. As they said there that anyone who eats something outside the place of its eating is [considered], “You may not eat in your gates.” And their intention, may their memory be blessed, in saying, “The verse only comes,” is to say that this is also included.

It is from the roots of the commandment to eat every sacrifice in its place so that its eaters will focus their hearts on the atonement for which they are eating. And it is like the matter that they, may their memory be blessed, said (Pesachim 59b), “The priests eat, and the owners are atoned.” And if they ate them in other places, their focus would be dissipated from the matter. This thing is well-known and clear.

The laws of the commandment are in Zevachim. (See Mishneh Torah, Laws of Sacrificial Procedure 11.)

And this prohibition is practiced in every place and at all times. As even one who consecrated a sin-offering or a guilt-offering today and transgressed and ate a kazayit from them — even the priests — is liable for lashes from this negative commandment, besides the prohibition that [exists] in deriving benefit from the consecrated. (See Kiddushin 57b.)