Zevachim 17A

אלא איכא למיפרך הכי ואיכא למיפרך הכי, כל חדא וחדא תיקו בדוכתיה.

Rather, one can derive this way and one can derive that way. Since these derivations contradict one another, each and every halakha should stand in its place and not modify the other by a fortiori inference.

טבול יום מנלן? דתניא, רבי סימאי אומר: רמז לטבול יום שאם עבד חילל ⁠– מנין? תלמוד לומר: ״קדשים יהיו ולא יחללו״;

§ The Mishnah teaches that sacrificial rites performed by one who immersed that day are disqualified. The Talmud asks: From where do we derive this halakha? The Talmud answers: It is derived as it is taught in a baraita that R' Simai says: From where in the Torah is the allusion with regard to a priest who immersed that day, that if he performed the Temple service he desecrated that service? It is derived from a verse, as the verse states: “They should be sacred to their God and they should not desecrate the name of their God” (Leviticus 21:6).

אם אינו ענין לטמא ⁠– דנפיק מ״וינזרו״, תנהו ענין לטבול יום.

If this verse is not written with regard to the matter of an impure priest who performed the Temple service, as that halakha is derived for us from the verse: “That they separate themselves from the sacred items of the children of Israel” (Leviticus 22:2), then apply it to the matter of a priest who immersed that day who performed the Temple service. Although he is no longer impure in every sense, the priest remains impure in the sense that he is prohibited from partaking of teruma and sacrificial food, and from entering the Temple.

אימא: תנהו ענין לקורח קרחה, ולמשחית פאת זקן!

The Talmud asks: Why must the verse be applied to the matter of one who immersed that day? Say that one should apply it to the matter of one who creates a bald spot upon his head or to the matter of one who destroys his beard, as these matters are discussed in the preceding verse.