Pesachim 98B

גמ׳ והא קא מייתי קדשים לבית הפסול?

Talmud: The Talmud challenges R' Shimon’s statement permitting priests to eat a Paschal lamb that became intermingled with firstborn animals: How can all of the animals be eaten according to the strictures of the Paschal lamb? They will cause offerings to be considered disqualified unnecessarily. A firstborn animal may be eaten for two days and one night while a Paschal lamb must be eaten in one night; therefore, eating the firstborn animals according to the strictures of the Paschal lamb will cause them to be disqualified and burned once morning arrives, despite the fact that they are not actually disqualified yet.

רבי שמעון לטעמיה, דאמר: מביאין קדשים לבית הפסול. דתנן: אשם שנתערב בשלמים ⁠— רבי שמעון אומר: ישחטו בצפון, ויאכלו כחומר שבהן.

The Talmud answers: R' Shimon conforms to his standard line of reasoning, as he said that it is permitted to cause offerings to be considered disqualified, as we learned in a Mishnah: If a guilt-offering became intermingled with a peace-offering, what should be done? R' Shimon says: One should slaughter all of them in the northern part of the Temple courtyard, like a guilt-offering, because it is permitted to slaughter a peace-offering there, even though it is not obligatory to do so. And they should be eaten as the stricter of them would be, according to the rules of a guilt-offering, which is a sacrifice of the most sacred order. Therefore, they must be eaten in the Temple courtyard over the course of one day and night, unlike sacrifices of minor sanctity, and may not be distributed to family members of the priests anywhere in Jerusalem.

אמרו לו: אין מביאין קדשים לבית הפסול.

The Rabbis said to him: One may not cause offerings to be considered disqualified, and since one of the animals is a peace-offering one may not treat it as a guilt-offering, which minimizes the time period in which it may be eaten and which may lead to it being burned unnecessarily. This indicates that R' Shimon is not concerned with this possibility.