הלכה על פסחים 9:21

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).