Here we have another testimony in the chapter, given by Rabbi Yehoshua and Rabbi Tzadok. Both were among the Sages of the Yavneh period. Rabbi Tzadok is the one who fasted for forty years before the destruction, and one of the three requests that Rabban Yochanan ben Zakkai made was that a doctor be brought to heal him. Their testimony concerns the laws of redeeming a firstborn donkey.
The mitzvah of redeeming a firstborn donkey:
If a person's donkey gives birth to a firstborn male, he is commanded to redeem it with a sheep - a goat or a lamb - and to give the sheep to a kohen, while the donkey remains in his possession. If he does not wish to redeem it, the only option available to him is to break the donkey's neck from behind, and the donkey is forbidden to derive any benefit from at all. It follows that the practical course is redemption.
The question before us:
What is the law if, after he redeemed the firstborn donkey with a sheep, that sheep died? Is the owner responsible to replace it with another sheep and give it to the kohen? On this question there are two sources that point in opposite directions:
Redemption of the firstborn son: a law very close to the redemption of a firstborn donkey. The father redeems his firstborn son with five sela'im - five silver coins - and gives them to a kohen. If the coins were lost after the redemption, the father must bring other coins and give the money to the kohen.
Redemption of Maaser Sheni: produce of years one, two, four and five of the Shemittah cycle - if one wishes to eat it outside Jerusalem, he first redeems its sanctity onto coins, brings the coins up to Jerusalem and eats with them there, and then the produce may be eaten outside Jerusalem. There, if the coins were lost after the redemption, there is no obligation to replace them.
The question, then, is whether there is an obligation of responsibility and replacement for one whose sheep was lost or died before he handed it over to the kohen, and on this the Sages disagreed.
The wording of the Mishnah:
"He'idu Rabbi Yehoshua v'Rabbi Tzadok al pidyon peter chamor shemes, she'ein bo lakohen kelum" - a sheep with which a firstborn donkey was redeemed and which then died: the kohen has no claim to it, and there is no obligation to replace it. The carcass itself is given to the kohen, and he may do with it as he wishes - use its hide or feed it to his dogs - but with that the matter ends. No body, no claim.
The root of the dispute:
"SheRabbi Eliezer omer chayav b'achrayutan" - in his opinion there is an obligation to replace it, and he must give the kohen the value of a live sheep, and therefore he brings a new sheep. And this is "k'chamesh sela'im shel ben" - just as one must replace five silver sela'im that were used to redeem his son and were lost.
"VaChachamim omrim ein chayav b'achrayutan, ela k'pidyon maaser sheni" - and this is the view of Rabbi Yehoshua and Rabbi Tzadok, that there is no obligation to replace a sheep that was lost or died after the redemption was performed with it, since the case resembles the money of Maaser Sheni redemption, which need not be replaced if it is lost.
The basis of the dispute in the verses:
The redemption of a firstborn donkey is juxtaposed in the Torah to the redemption of a firstborn son: "ufeter chamor tifdeh veseh" - "and the firstling of a donkey you shall redeem with a lamb," and shortly afterward, "kol bechor banecha tifdeh" - "every firstborn of your sons you shall redeem." The question is whether this juxtaposition, the comparison drawn between them, teaches that the law of one carries over to the other. In the opinion of Rabbi Eliezer, the juxtaposition teaches that here too the lamb must be replaced.
Rabbi Yehoshua and Rabbi Tzadok, and likewise the Sages, hold that this is not so, based on another verse in Bamidbar: "ach padoh sifdeh es bechor ha'adam ve'es bechor habeheimah hatemei'ah tifdeh" - "but you shall surely redeem the firstborn of man, and the firstborn of an impure animal you shall redeem." The word "ach" is a term of limitation, and it comes to limit the scope of the connection between the redemption of the donkey and the redemption of a person.
That is, in certain respects the two are indeed linked to one another: a Levi or a kohen who has a firstborn son need not redeem him, and likewise a Levi or a kohen who owns a firstborn donkey need not redeem it. But in other respects they are not equal: in the redemption of a person there is responsibility to replace five coins that were lost, whereas in the redemption of a firstborn donkey there is no obligation to replace a lamb that died or was lost after the redemption had already taken effect.
In summary: in this testimony Rabbi Yehoshua and Rabbi Tzadok teach that when the lamb used to redeem a firstborn donkey dies, the kohen receives nothing. Rabbi Eliezer holds the owner responsible, based on the juxtaposition of the verses to the redemption of the firstborn son, while the Sages exempt him and compare it to the money of the redemption of maaser sheni, deriving this limitation from the word "ach" in the verse.