Zevachim 70A

האי נמי תיפוק לי מ״וחלב נבלה״⁠ –

The Talmud challenges: According to this logic, one can also derive the halakha that the forbidden fat of the carcass of a non-kosher animal is impure from the verse: “And the fat of a carcass, and the fat of a tereifa, may be used for any other service” (Leviticus 7:24), which teaches that such forbidden fat is ritually pure.

מי שאיסורו משום בל תאכל חלב נבלה; יצאתה זו שאין איסורה משום בל תאכל [חלב נבלה], אלא משום טמא!

The continuation of the verse: “But you should in no way eat of it,” indicates that the verse renders pure only fat that is forbidden specifically due to the prohibition: You should not eat the forbidden fat of a carcass, i.e., the forbidden fat of kosher animals. This serves to exclude this forbidden fat of a non-kosher animal, which is not forbidden due to the prohibition: You should not eat the forbidden fat of a carcass, but rather due to the prohibition against eating a non-kosher animal. Since the verse that states that fats are ritually pure is referring only to kosher animals, the forbidden fat of a carcass of a non-kosher animal must be impure. Rav Sheizevi’s derivation of this halakha from the word tereifa is therefore superfluous.

אלא האי טריפה מיבעי לאיתויי חיה ⁠– סלקא דעתך אמינא: מי שחלבה אסור ובשרה מותר, יצאת זו שחלבה ובשרה מותר; קא משמע לן.

Rather, this word “tereifa” is necessary to include the forbidden fat of a carcass of a kosher undomesticated animal, to teach that it is ritually pure; as it might enter your mind to say that only the forbidden fat of carcasses of those animals whose fat is forbidden and whose meat is permitted if slaughtered, i.e., kosher livestock, is ritually pure, and this serves to exclude this forbidden fat of carcasses of those animals whose fat and meat are both permitted if slaughtered, i.e., kosher undomesticated animals, whose fat is impure. To counter this possibility, the word “tereifa” teaches us that the fat of a carcass of any animal that can become a tereifa is ritually pure, including the fat of kosher undomesticated animals.