Midrash sur Les Nombres 18:15

Which thou hast. This excludes the animals that are still in the embryonic state when sold to a gentile. Is the one who purchases an animal in the embryonic state obligated to consecrate it? Scripture answers this question with the verse All the firstling males that are born of thy flock and thy herd, those thou shalt sanctify unto the Lord (Deut. 15:19). (This tells us no.¹⁹The embryo was conceived before the sale was made.) The males shall be the Lord’s (Exod. 13:12). R. Yosé stated: You learn from this that if an ewe, which had not given birth previously, bears twin males, they both belong to the priest, since it is said: The males shall be the Lord’s. Every firstling of an ass, thou shalt redeem with a lamb (Exod. 13:12); but not with a calf or with a wild beast, or with a ritually slaughtered animal, or with hybrids, or with a koy.²⁰An antelope or bearded deer. The rabbis were in doubt as to whether it is considered a domesticated animal or a wild beast. The firstling of an ass you may redeem, but not with any other animal. What is meant by Thou shalt surely redeem? You may redeem the firstling of an ass with any impure animal only if it is to be sanctified for the purpose of the upkeep of the Temple.

All the firstborn of man among thy sons shalt thou redeem is a general statement, and According to thy evaluation, five shekels of silver (Num. 18:16) is a particular statement. And nothing may be attributed to the general statement that is not included in the particular. But when another general statement follows the preceding verse, The firstborn of man shalt thou redeem (Num. 18:15), we have an instance of a general statement and a particular one followed by another general statement, which must be considered to include anything resembling that which is stated in the particular.²²The sixth of Rabbi Ishmael’s thirteen rules. In this case the particular statement stipulates movable property that has no permanency, and so the general statement must refer to movable property that has no permanency. From this the sages concluded that the firstborn of man may be redeemed with anything except slaves, bonds, or land, for they have permanency. All the firstborn of man among thy sons (Exod. 13:13). If a man has five wives who were virgins, and they gave birth to five sons, must he redeem them all? Yes, for All that openeth the womb that is a male—thou shalt redeem. The Holy One, blessed be He, said: The firstlings are the priest’s property and are not considered as a gift. Why did Scripture need to say: All the firstborn among thy sons thou shalt redeem? To point out that if a man’s father did not redeem him, he must redeem himself. From this you learn that a man is obligated to teach his son the Torah, but if the father does not instruct him, he must study by himself. This may be deduced logically from the subject of redemption.

(Exodus 13:13) "and every firstling of an ass shall you redeem with a lamb": And not with a calf, and not with an animal, and not with a slaughtered (beast) and not with a treifah, and not with a koi (a creature that is not clearly "beast" or "animal") and not with kilayim (a hybrid). (Ibid. 34:20) "And the firstling of an ass you shall redeem": What is the intent of this? From (Numbers 18:15) "but redeem shall you redeem the first-born of the man, and the first-born of the unclean beast," I might think that every unclean beast is understood. It is, therefore, written (Exodus 13:13) "and every firstling of an ass you shall redeem with a lamb." It is an ass that you redeem, and not the firstling of other unclean beasts. But still I would say: It is the firstling of an ass that you redeem with a lamb, and the firstling of other unclean beasts, with garments or vessels. It is, therefore, written (Ibid. 34:20) "And the firstling of an ass, etc." It is the firstling of an ass that you redeem and you do not redeem the firstling of any other unclean beast. What, then, is the intent of (Numbers 18:15) "but redeem shall you redeem, etc."? If it cannot apply to redeeming an unclean beast, understand it as indicating that one may dedicate an unclean beast to the department for Temple maintenance and redeem it thence.