Bekhorot 6A

תלמוד לומר: ״פטר חמור״ ״פטר חמור״ שני פעמים ⁠— פטרי חמורים אמרתי לך, ולא פטרי סוסים וגמלים.

Therefore, the verse states the phrase: “Firstborn of a donkey” (Exodus 13:13), “firstborn of a donkey” (Exodus 34:20), mentioning it a total of two times. The additional usage of the term indicates I said to you that firstborn status applies only to firstborns of donkeys, but not to firstborns of horses or camels.

פריך רב אחאי: אי כתב רחמנא חד, הוה אמינא דבר שהיה בכלל, ויצא מן הכלל ללמד, לא ללמד על עצמו יצא אלא ללמד על הכלל כולו יצא, ולעולם בשה.

Rav Aḥai refutes this claim: How can the extra verse alone indicate that other firstborn non-kosher animals do not have firstborn status? If God had written the term “firstborn of a donkey” once, I would say a firstborn donkey is an item that was included in a generalization of all non-kosher animals, but emerged from the generalization to teach that it must be redeemed by means of a lamb. According to the principles of exegesis, it emerged from the generalization to teach not just about itself, but emerged to teach about the entire generalization. And accordingly, all non-kosher animals should actually be redeemed by means of a lamb as well.

כתב רחמנא ״פטר חמור״ אחרינא, פטרי חמורים ולא פטרי סוסים וגמלים, ואימא: מעטינהו משה, ולעולם בכל דבר!

Therefore, God writes: “Firstborn of a donkey,” another time, to teach that only firstborn donkeys must be redeemed by means of a lamb, but not firstborn horses or camels. And therefore I can say that perhaps the earlier suggestion is correct: The Torah excluded firstborn horses and camels from being redeemed by means of a lamb, but actually, they must still be redeemed by means of any other item.

אם כן, לכתוב רחמנא: ״פטר חמור תפדה בשה״ ו״חמור תפדה בשה״. ״פטר חמור תפדה בשה״, ״פטר חמור תפדה בשה״ למה לי? פטרי חמורים אמרתי לך, ולא פטרי סוסים וגמלים.

The Talmud answers: If it is so that the Torah excludes horses and camels only from redemption by means of a lamb but not from redemption in general, let God write: Firstborn of a donkey you should redeem with a lamb, and: A donkey you should redeem with a lamb, which would suffice. Why do I need the verse to state: “A firstborn of a donkey you should redeem with a lamb,” “a firstborn of a donkey you should redeem with a lamb,” using the same phrase both times? It is necessary to teach that I said to you that firstborn status applies only to firstborns of donkeys, but not to firstborns of horses or camels.