Bekhorot 28A

ואידך, אי מהתם איכא למימר חזה ושוק של תודה.

And the other ones, i.e., the rabbis from the school of Rav, why don’t they derive the halakha that a firstborn is eaten for two days and one night from that verse? The Talmud answers that if it were derived from there, it would be possible to say that the verse is comparing the halakha of a firstborn to the breast and thigh of a thanks offering, which are eaten for only one day and night.

ואידך, אמר קרא: ״לך יהיה״⁠ — הוסיף לך הכתוב הויה אחרת בבכור.

The Talmud asks: And the other one, Rav Yehuda, citing Rav, how does he respond to this? The verse states: “And their flesh should be yours, as the breast of waving and as the right thigh, it should be yours” (Numbers 18:18). The verse adds another mention of a form of the term being in the second phrase: “It should be yours,” to teach that the priest has an additional day to eat a firstborn animal, i.e., that it is compared to the breast and thigh of a peace offering, not to that of a thanks offering.

ואידך, הא מהתם איכא למימר: האי ״יהיה לך״⁠ — לימד על בכור בעל מום שנותנו לכהן, שלא מצינו לו בכל התורה כולה.

The Talmud asks: And the other ones, the rabbis from the school of Rav, how do they respond to this claim? The Talmud answers: With regard to the inference from there, it is possible to say that this phrase: “It should be yours,” teaches with regard to a blemished firstborn that the owner must give it to the priest. This derivation is necessary, as we have not found this halakha that a blemished firstborn is given to a priest stated explicitly anywhere in the entire Torah.