Bekhorot 12B

לרבי שמעון נמי, ״צבי ואיל״ כתיב בהו.

according to R' Shimon as well, perhaps one cannot redeem a firstborn donkey with disqualified consecrated animals, as it is written with regard to them that they are to be treated: “Like the gazelle and like the hart” (Deuteronomy 12:15). Since a gazelle and a hart cannot be used for redemption, so too, disqualified consecrated animals cannot be used for redemption.

איבעיא להו: מהו לפדות בבהמת שביעית?

§ A dilemma was raised before the rabbis: What is the halakha with regard to redeeming a firstborn donkey with an animal that was purchased with produce of the Sabbatical Year, which caused the sanctity of the produce to be transferred to the animal?

ודאי ⁠— לא תיבעי לך, לאכילה אמר רחמנא, ולא לסחורה. כי תיבעי לך ⁠— ספק.

The Talmud clarifies the question: With regard to redeeming a donkey that has definite firstborn status with an animal that was purchased with produce of the Sabbatical Year, you should not raise the dilemma, as one certainly may not redeem it in this manner, since the owner acquires his firstborn donkey in exchange for the animal that he gives to the priest, and this is prohibited with regard to such an animal. This is because God states with regard to the Sabbatical Year: “The rest of the land should be for you for consumption” (Leviticus 25:6), indicating that the produce may be used for consumption but not for commerce. Rather, when should you raise the dilemma? Raise it in the case of a donkey with uncertain firstborn status.

ואליבא דרבי שמעון לא תיבעי לך, דלית ליה ספק, כי תיבעי לך אליבא דרבי יהודה.

The Talmud clarifies further: And according to the opinion of R' Shimon you should not raise the dilemma, as he does not hold that redemption is necessary in the case of a donkey with uncertain firstborn status. When should you raise the dilemma? Raise it according to the opinion of R' Yehuda, who holds that in such a case the owner of the donkey must designate a lamb for its redemption in order to abrogate its forbidden status, but he is not required to give it to a priest.