Bekhorot 12A

מתני׳ אין פודין לא בעגל ולא בחיה, לא בשחוטה ולא בטריפה, ולא בכלאים ולא בכוי. ורבי אליעזר מתיר בכלאים מפני שהוא שה, ואוסר בכוי מפני שהוא ספק. נתנו לכהן ⁠— אין הכהן רשאי לקיימו עד שיפריש שה תחתיו.

Mishnah: One may not redeem a firstborn donkey, neither with a calf, nor with an undomesticated animal, nor with a slaughtered animal, nor with a tereifa, nor with a hybrid of a sheep and a goat, nor with a koy, which is an animal with regard to which it is uncertain whether it is domesticated or undomesticated. And R' Eliezer deems it permitted to redeem a firstborn donkey with a hybrid of a sheep and a goat, because it is a lamb, i.e., that hybrid has the status of a lamb, but prohibits redeeming it with a koy, because its status is uncertain. If one gave the firstborn donkey to a priest, the priest may not keep it unless he first designates a lamb in its stead for redemption.

גמ׳ מתניתין מני? בן בג בג היא, דתניא: בן בג בג אומר: נאמר כאן ״שה״, ונאמר להלן ״שה״, מה להלן פרט לכל השמות הללו, אף כאן פרט לכל השמות הללו.

Talmud: Whose opinion is expressed in the first clause of the Mishnah? It is the opinion of ben Bag Bag, as it is taught in a baraita that ben Bag Bag says: It is stated here, with regard to the redemption of a firstborn donkey: “And you should redeem a firstborn donkey with a lamb” (Exodus 13:13), and it is stated there, with regard to the Paschal offering: “In the 10th day of this month they should take to them every man a lamb” (Exodus 12:3). By inference, just as there, with regard to the Paschal offering, the Torah excludes all of these names, i.e., all of these types of animals listed in the Mishnah, from being fit for sacrifice as a Paschal offering, so too here, with regard to the redemption of a firstborn donkey, the Torah excludes all of these names.