Tosafot: On the Babylonian Talmud, Tractate Avodah Zarah

A Jew may not say to a non-Jew: Take your portion for the Sabbath, and I my portion for the weekdays. [b. Avodah Zarah 22a]

[My father,] R. [Isaac of Dampierre], was asked about a certain oven. A Jew owned at least half of it having received it [as payment] for a debt from a non-Jew. Now the non-Jew, a baker, maintained a portion in the profits from the oven, and [the stipulation] was that the Jew would take [the profits of] such-and-such days, and the non-Jew such-and-such. [The question was,] may the Jew say to the non-Jew, “You take your portion on the Sabbath and I my portion for the weekdays,” in a case where they had not made [such] a prior stipulation, [that] “the day of the Sabbath will be yours [the non-Jew’s] and I will take in its place one of the weekdays.”

R. [Isaac] said that there are grounds to permit [this], because, even though [this passage from b. Avodah Zarah] prohibits this in the case of a Jew and a non-Jew who received a field in partnership, that [ruling] applies specifically to a field, as the entire field is enhanced by the labor that the non-Jew performs on the Sabbath. Furthermore, if the non-Jew never worked at all, the Jew’s portion would not be worth as much. Here, however, [regarding an oven], the Jew’s portion on the weekday does not decrease at all if the non-Jew does not perform labor on the Sabbath. And if [the non-Jew] does [work on the Sabbath,] the Jew’s portion is not thereby enhanced at all. Consequently, perhaps [the Jew] may be able to say to [the non-Jew], “Take your portion on the Sabbath, etc.” But Rabbenu Tam replied to [my father] that there is no difference between an oven and a field, and in all cases we prohibit [the practice], for it is [considered] as though [the Jew] is actively setting up a [non-Jewish] worker on the Sabbath, and telling him, “Perform labor on the Sabbath,” and telling a non-Jew [to perform a forbidden labor on the Sabbath is prohibited, as] a rabbinic prohibition.

In my opinion this should be prohibited, as the Jew is effectively renting out his oven on the Sabbath, as he says to the non-Jew, “Use my oven for yourself, and toil today as my baker on the weekday, in place of what you earn on the Sabbath, from the work that I am telling you to perform for yourself,” as the oven is in the Jew’s possession on the day of the Sabbath in partnership, because they did not stipulate [otherwise] from the outset. It turns out that [the non-Jew] is selling him the Sabbath labor with his oven in order to work for him on the weekdays in his stead. And R. [Isaac] agreed.

According to my explanation, namely, that it is prohibited in [the case of] an oven because one accepts the wage of Sabbath [labor] with his [own] oven, it seems to me that it should be prohibited even if they made a prior stipulation, since the non-Jew has no portion in the oven, and it cannot be said that [the oven] is owned by the non-Jew on the Sabbath and by the Jew on another corresponding day of the week. It is permitted only if ownership is transferred to the non-Jew such that it is always his own on the Sabbath, in which case a prior stipulation is effective.

In practice, Rabbenu Jacob [Tam] ordered the [Jewish] oven owner—the lender—to return his debt from the non-Jew and lend him [the money] again with the prior stipulation.

Later, R. [Isaac] found proof that it is prohibited, and that there is no difference between a field and another item that is not improved, such as an oven or bathhouse. As it is explicitly taught in the Tosefta of Demai [6:3], [in the] chapter [that begins] “One who receives a field”: A convert and a non-Jew who inherited from their father, etc. And it is taught [b. Avodah Zarah 21b]: A Jew and a non-Jew who acquired a bathhouse in partnership, the Jew may not say to the non-Jew, “Take your portion on the Sabbath, and I my portion for the weekdays, etc.”