출애굽기 34:20 미슈나 참조: Mishnah Bekhorot, Mishnah Bikkurim & Mishnah Eduyot

If a cow gave birth to a species of donkey, or a donkey gave birth to a species of horse, it is exempt from [the law of] the firstling, for it is said, “the firstling of a donkey,” “the firstling of a donkey,” twice [to teach that the law of the firstling does not apply] until that which gives birth is a donkey and that which is born is a donkey. And what is the law with regard to eating them? If a clean animal gave birth to a species of unclean animal, it is permitted to be eaten. But if an unclean animal gave birth to a species of a clean animal, it is forbidden to be eaten, for that which comes out of the unclean is unclean and that which comes out of the clean is clean. If an unclean fish swallowed a clean fish, it is permitted to be eaten. But if a clean fish has swallowed an unclean fish, the latter is forbidden to be eaten, because it is not [the clean fish's] growth.

If one donkey had given birth before and one had not given birth before and they gave birth to two males, he gives one lamb to the priest. [If they gave birth to] a male and a female, he sets aside one lamb [which he keeps] for himself. For it says, “And the firstling of a donkey you shall redeem with a lamb” (Exodus 34:20), [the lamb can come either] from the sheep or the goats, male or female, large or small, unblemished or blemished. He can redeem with the same lamb many times. [And the lamb] enters the pen to be tithed. If it dies [before he gives it to the priest], he can benefit from it.

If he does not wish to redeem it, he breaks its neck from behind with a large knife and buries it. The mitzvah of redemption takes priority over the miztzah of breaking its neck, for it says: “And if you don’t redeem it, you must break its neck” (Exodus 13:13). The mitzvah of designation takes priority over the mitzvah of redemption, for it says: “Who has betrothed her to himself, he must let her be redeemed” (Exodus 21:8). The mitzvah of yibbum is prior to the mitzvah of halitzah. [This was so] at first when they intended to carry out the mitzvah. But now that they do not intend to carry out the mitzvah, the [rabbis] have said: the mitzvah of halitzah takes priority over the mitzvah of yibbum. The mitzvah of redemption [of an unclean animal whose value has been dedicated to the Temple] is upon the owner. He takes priority over any other man, for it says: “If it is not redeemed, then it shall be sold according to your evaluation” (Leviticus 27:27).