Maaser Sheni, Chapter 3, Mishnah 10. In the previous mishnah we learned that maaser sheni that became tamei may be redeemed even in Jerusalem. Our mishnah deals with a further case: not with maaser sheni itself, but with produce purchased with maaser sheni money that then became tamei.
The text of the Mishnah:
"HaLokeach peiros b'chesef maaser sheni shenitme'u - yipadu" - this is the opinion of the first Tanna: food that was bought with maaser sheni money and became tamei may be redeemed.
"Rabbi Yehudah omer: yikaver" - according to Rabbi Yehudah there is no remedy for this produce other than covering it over and burying it, and there is nothing else that can be done with it; since it was bought with maaser sheni money, there is no longer any possibility of redeeming it. The source of this ruling is the verse "v'tzarta hakesef" - that one must bind up the money and use it for redemption, from which we learn that the Torah refers to the first money and not to a second round of money. There is only one redemption here, and one does not redeem a second time.
The Sages' argument - a kal vachomer:
The Sages said to Rabbi Yehudah: "Umah im maaser sheni atzmo shenitma harei hu nifdeh" - if maaser sheni itself that became tamei is redeemed, as we learned in the previous mishnah, then all the more so with produce that is not actual maaser sheni but was merely purchased with maaser sheni money and became tamei - "eino din sheyipadu?" Surely it is only right to permit its redemption.
Rabbi Yehudah's response:
Rabbi Yehudah answered them that this is not a valid kal vachomer: "Im amarta b'maaser sheni atzmo... shekein hu nifdeh b'tahor b'richuk makom" - with maaser sheni itself there is a halachah that when it is tahor and is located at a distance from Jerusalem, it may be redeemed for money. It is possible, then, that because of this leniency the Sages were lenient with it even when it became tamei in Jerusalem. But "tomar b'chesef maaser sheni, she'eino nifdeh b'tahor b'richuk makom" - produce that was bought with maaser sheni money has no share in this halachah at all, and even when it is tahor and located far from Jerusalem it cannot be redeemed.
For someone who redeemed his maaser with money and then bought produce with it is bound by the halachah - as we learned in the first chapter - that he must bring the produce up to Jerusalem and eat it there, and he may not redeem it a second time. It emerges that produce bought with maaser sheni money is treated more stringently than the maaser itself in this respect. For this reason Rabbi Yehudah holds that one cannot apply a kal vachomer to it regarding redemption after it became tamei, and therefore its only ruling is burial.
In summary: In this mishnah there is a dispute about produce bought with maaser sheni money that became tamei: according to the first Tanna it is redeemed, and according to Rabbi Yehudah it is buried, since from the verse "v'tzarta hakesef" we learn that redemption applies only to the first money. The Sages sought to derive a kal vachomer from maaser sheni itself, which is redeemed when it becomes tamei, and Rabbi Yehudah rejected the kal vachomer: maaser sheni itself is redeemed even when it is tahor and at a distance from Jerusalem, whereas produce bought with maaser sheni money is not redeemed at all but must be brought up and eaten in Jerusalem - and therefore it is more stringent, and one cannot derive a leniency from it.