Yoma 83B

אפשר בחולין ⁠— פשיטא? לא צריכא, בשבת.

It was stated that, according to Rabba, if it is possible to make the untithed produce fit and then feed him with non-sacred food, one should do so. The Talmud is surprised at this: It is obvious that if it is possible to tithe the produce and feed him that, one should do so. Why must it be stated? The Talmud explains: No, it is necessary to state this with regard to a case on Shabbat, when it is generally prohibited to separate terumot and tithes. Even so, the rabbis said that it is better to separate terumot and tithes on Shabbat rather than feed the ill person untithed produce.

בשבת נמי, פשיטא ⁠— טלטול מדרבנן הוא! הכא במאי עסקינן ⁠— בעציץ שאינו נקוב, דרבנן.

The Talmud asks: With regard to Shabbat it is also obvious, since the prohibition against separating terumot and tithes is merely a prohibition against moving, which is prohibited by rabbinic law. That is certainly less severe than the prohibition against eating untithed produce. The Talmud answers: With what are we dealing here? We are dealing with fruits grown in an imperforate container, which are not subject to teruma by Torah law but by rabbinic law. The Talmud teaches that it is preferable to transgress the rabbinic prohibition of tithing the fruit on Shabbat rather than feed the ill person untithed produce, although in this case the prohibition is rabbinic.

מר סבר טבל חמור, ומר סבר תרומה חמורה.

§ The Talmud now discusses the aforementioned two opinions: One Sage, ben Teima, holds that untithed produce is more severe, and therefore one must tithe the fruit although it is prohibited to separate teruma on Shabbat; and one Sage, the first tanna, holds that teruma is more severe.