Pesachim 45A

משום דהוה נזיר וחטאת שני כתובין הבאין כאחד, ואין מלמדין.

due to the fact that the halakhot of a nazirite and those of a sin-offering are two verses that come as one, i.e., to teach the same principle, and two verses that teach the same principle do not teach that principle by analogy.

נזיר, הא דאמרן. חטאת מאי היא? דתניא: ״כל אשר יגע בבשרה יקדש וגו׳״, יכול אפילו לא בלעה? תלמוד לומר: ״בבשרה (יקדש)״⁠ — עד שיבלע בבשר

The Talmud elaborates: The derivation that a permitted substance joins together with a prohibited substance in the case of a nazirite is that which we stated above. With regard to a sin-offering, what is the derivation that permitted material combines with prohibited material? As it was taught in a baraita with regard to the verse: “Anything that touches in its flesh should become consecrated” (Leviticus 6:20). I might have thought that non-sacred meat that touched any part of a sin-offering is rendered prohibited even if it did not absorb the taste of the sin-offering it touched. Therefore, the verse states: In its flesh should become consecrated, to teach that this meat is not consecrated until the taste of the sin-offering is absorbed within its flesh.

״יקדש״⁠ — להיות כמוה, שאם פסולה היא ⁠— תיפסל, ואם כשירה היא ⁠— תאכל כחמור שבה.

The baraita continues: should become consecrated means that its legal status becomes like that of the sin-offering itself; that is, if the sin-offering is disqualified, this meat will also be disqualified. And if the sin-offering is valid, the meat that touched it may be eaten in accordance with the more stringent standards of a sin-offering as far as when and where it may be eaten. The principle that a permitted substance joins together with a prohibited substance applies in the case of a sin-offering as well. Therefore, the principle cannot be extended to the entire Torah, as a halakha stated in two cases is not applied elsewhere.