And the 118th prohibition is that we are forbidden from leaving over any meat from the Chagigah (Festive Offering) which is offered on the 14th [of Nissan], until the third day, as is explained in the 6th chapter of Pesachim.1 One must eat it in the course of two days.
The source of this commandment is G‑d's statement,2 "Do not let the meat that you sacrificed in the evening of the first day remain overnight until morning." The Oral Tradition3 on this verse explains, "The verse, 'Do not let the meat [that you sacrificed in the evening of the first day] remain overnight [until morning],' means that the Chagigah which is brought together with the Pesach offering must be eaten within two days. One might think [it must be eaten] within one day; when the verse says the [seemingly superfluous phrase,] 'until morning,' it means the morning of the second day."
It is regarding this [offering] that the Torah says,4 "You shall sacrifice the Passover offering to G‑d your L‑rd, [along with other] sheep and cattle."
Anything left over from this Chagigah of the 14th [of Nissan] until the third day must be burned in fire, since it is included in [the category of] notar ("Left over" past its prescribed time).5 For this reason,6 one is not punished by lashes for it (When a negative command prescribes a remedial action, no punishment is commanded).
The details of this mitzvah — i.e. the Chagigah of the 14th7 [of Nissan] — are explained in many passages in tractate Pesachim8 and tractate Chagigah.9