Temurah 20A

ולפסחו ולאשמו ⁠— עושה תמורה.

or for his Paschal offering or for his guilt offering, although these offerings are brought only from male animals, it is still consecrated with inherent sanctity. Therefore, if one exchanges for it a non-sacred animal, he renders that animal a substitute, which is consecrated with the same sanctity as the original animal.

רבי שמעון אומר: לעולתו ⁠— עושה תמורה, לפסחו ולאשמו ⁠— אין עושה תמורה.

R' Shimon disagrees with the rabbis and says: The halakha is not the same in all these cases. Granted, if he consecrates a female animal for his burnt offering, it renders the non-sacred animal that is exchanged for it a substitute, as there is burnt offering status for female birds. For this reason it is consecrated with inherent sanctity and can be sold only after it has become blemished. But if he consecrates a female animal for his Paschal offering or for his guilt offering it is not consecrated with inherent sanctity, and it may be sold even without a blemish. Therefore, it does not render the non-sacred animal that is exchanged for it a substitute.

שאין לך דבר עושה תמורה, אלא הרועה להסתאב.

This ruling is based upon the principle that no animal renders the non-sacred animal that is exchanged for it a substitute except for an animal that has inherent sanctity, which means that even if it may not be sacrificed, it must still be left to graze in order to become blemished, after which it is sold, and the proceeds from the sale are used to purchase a fit offering.

אמר רבי: אין אני רואה דבריו של רבי שמעון בפסח, הואיל ומותר הפסח קרב שלמים.

R' Yehuda HaNasi says, with regard to this dispute between R' Shimon and the first tanna: I do not agree with the statement of R' Shimon with regard to the Paschal offering, that a non-sacred animal exchanged for a female which was designated for a Paschal offering does not become consecrated as a substitute. I disagree, since a leftover Paschal offering is sacrificed after Passover as a peace offering, and a peace offering is brought even from female animals. Therefore, a female animal that was designated for a Paschal offering should be consecrated with inherent sanctity, as there is peace offering status for female animals. It should not be sold unless it has a blemish, and it should render a non-sacred animal that is exchanged for it a substitute.