Halakhah к Шмот 23:18

That we not slaughter the lamb of the Pesach offering on the fourteenth of Nissan while chamets is still in our possession: That we not slaughter the lamb of the Pesach offering on the fourteenth of Nissan while chamets still be in our possession - until half of the day, as they, may their memory be blessed, expounded (Pesachim 5a),"[The word,] 'but,' divides" - as it is stated (Exodus 23:18), "Do not slaughter upon chamets the blood of my slaughtering." And the explanation of it comes [to tell us] not to slaughter the lamb of the Pesach sacrifice while chamets still exist in your possession. And this preventing is repeated in the Torah, with a different expression. And we have also understood that included in the explanation is that chamets not be with the one who slaughters it (Pesachim 13b) and not be with the one that sprinkles its blood and not be with the one that makes its fat smoke and not be with one of the assemblage that is counted upon it (Pesachim 63b).

To not leave the entrails of the Pesach sacrifice to stay overnight: Not to leave the entrails of the Pesach sacrifice until the morning, [such] that they not be sacrificed, and [so] become disqualified with this leaving over and become called notar (what is left over); as it is stated (Exodus 23:18), "and the fat of My festival offering shall not be left lying until morning." And the same is true of other portions to be burned in other sacrifices. And the language of Mekhilta d'Rabbi Yishmael 23:18 is "'The fat shall not be left lying' - the verse comes to teach that the fats are disqualified by lying over." And this preventing was already repeated in another place, as it is stated (Exodus 34:25), "and the sacrifice of the festival of Pesach shall not be left lying until morning."