Pesachim 63 - Clean up your act

On Passover, one should not own any chametz. If he is slaughtering the Passover offering while he still has some chametz, he is kind of adding insult to the injury and thus transgresses a separate prohibition of "you should not own any chametz while offering a sacrifice."

Now we get into some disagreements over the details. Rabbi Shimon qualifies that he only transgresses if he has the right intentions for the sacrifice. Otherwise, his sacrifice is invalid, and according to Rabbi Shimon, any slaughter that is not valid is not considered slaughter at all. Thus, he is not liable for an additional prohibition of slaughtering while owning chametz.

Furthermore, Resh Lakish says that the chametz must be with him in the Temple Courtyard. Why is that? - To be liable for any prohibition, one must receive a warning just before the act. If this chametz is not with him but is at his home, the witnesses giving the warning can never be sure that the chametz indeed exists in his possession. Therefore, their warning will be conditional, like "keep in mind that if you have chametz - then..." and conditional warnings do not count.

Art: Slaughtering by Jan Stobbaerts