Study Keritot folio 25A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
R' Yannai says: I heard an answer with regard to the boundary, i.e., the stage, beyond which it is prohibited, but I have forgotten what it is; and the members of the group of rabbis were inclined to say that its descent to the rough, dried-up stream, where its neck is broken, is the action that
Rav Hamnuna said: From where do I say that the prohibition takes effect when the animal is alive? I say it from that which we learned in a Mishnah (Ḥullin 81b): With regard to one who slaughters the red heifer of purification, or an ox that was sentenced to be stoned, or a heifer whose neck is broke
Rav Hamnuna explains his proof: Granted, according to my opinion, that I say the prohibition takes effect from the time when the animal is alive, R' Shimon and the Rabbis disagree with regard to this matter, as R' Shimon holds: Slaughter that does not render the animal fit for consumption is not con
Rav Hamnuna continues: And the Rabbis say: Slaughter that does not render the animal fit for consumption is considered slaughter, and therefore he is liable for the slaughter of a mother and its offspring. But if you say that the prohibition does not take effect until after the breaking of the neck
And if you would say the reason is that R' Shimon holds that one who performs the breaking of the neck of the heifer by slaughter has performed the mitzva in a fit manner, and consequently that slaughter rendered the heifer prohibited with regard to deriving benefit from it and it is therefore unfit