Yevamot 82A

רבי יהודה לטעמיה, דאמר: מין במינו לא בטיל.

The Talmud answers: R' Yehuda conforms to his standard line of reasoning, as he stated a principle that if a particular type of food is mixed with food of its own type, it cannot be nullified under any circumstances.

אבל לא נימוחה מאי ⁠— לא תעלה, אדתני: אבל חתיכה של חטאת טהורה שנתערבה במאה חתיכות של חולין טהורות לא תעלה, ניפלוג וניתני בדידה: במה דברים אמורים, בשנימוחה, אבל לא נימוחה ⁠— לא תעלה!

The Talmud asks further: But had the piece of meat not been crushed, what would the halakha be? Presumably, it would not be nullified. If so, there is a difficulty, as instead of teaching a case involving non-sacred meat in the second half of the baraita, as follows: However, if a piece of a ritually pure sin-offering became intermingled with 100 pieces of ritually pure non-sacred meat, the impure piece of a sin-offering is not nullified; let the tanna distinguish and teach it in the case involving only sacred meat, as follows: In what case is this statement said? It is in a case where the piece of meat has been crushed and broken into small parts, but if it has not been crushed, it is not nullified.

טהורות בטהורות עדיף ליה.

The Talmud answers: Even so, the tanna prefers to address the case of an intermingling of ritually pure items with other ritually pure items and thereby teach a novel halakha, notwithstanding the fact that he could have made a distinction within the case of a ritually impure piece itself.

ולריש לקיש, מאי שנא רישא ומאי שנא סיפא? אמר רב שישא בריה דרב אידי: רישא, בטומאת משקין דרבנן. סיפא, דאורייתא.

The Talmud asks: And according to Reish Lakish, who establishes the baraita as referring to a piece of meat that has been crushed, what is different in the first clause of the baraita and what is different in the latter clause? Why is nullification possible in the case of impure pieces, but not in the case of pure ones? Rav Sheisha, son of Rav Idi, said: The first clause is dealing with a piece of a sin-offering that contracted ritual impurity due to liquids, which is imparted by rabbinic law. Since the sacred food contracted impurity that is only rabbinic in origin, it may be nullified rather than allowed to go to waste. The latter clause, on the other hand, deals with sacred food that became intermingled with ordinary non-sacred food. The sacred food is forbidden to non-priests by Torah law, and therefore it is not nullified.