מעשה שבת ליתסרו דהא תיעבתי לך הוא then let the product of an action that desecrates Shabbat, e.g., food cooked on Shabbat, be prohibited for consumption, as desecration of Shabbat is a practice of which God states: I have made it abominable to you, in that it is prohibited to cook on Shabbat. How can this food be prohibited only to the one who cooked it as a penalty by rabbinic law, but be permitted to others (see 15a)?
אמר קרא (שמות לא, יד) כי קדש היא לכם היא קדש ואין מעשיה קדש The Gemara answers: A product of the desecration of Shabbat is an exception to the rule, as the verse states with regard to Shabbat: “For it is sacred to you” (Exodus 31:14). One may infer: It, Shabbat itself, is sacred, but the products of actions that desecrate it are not sacred, i.e., not prohibited.
חורש בשור ובחמור וחוסם פי פרה ודש בה ליתסרו דהא תיעבתי לך הוא The Gemara raises another difficulty: If one plows with an ox and with a donkey together, thereby violating the prohibition in Deuteronomy 22:10, or if one muzzles the mouth of a cow and threshes with it, thereby violating the prohibition in Deuteronomy 25:4, the seeds or threshed grain should be prohibited for consumption according to the above principle, as these are both practices I have made abominable to you.
השתא ומה שבת דחמירא מעשיה מותרים הני לא כל שכן The Gemara responds: Now that it has been established that products of desecration of Shabbat are permitted, one can derive the following using an a fortiori inference: Just as with regard to Shabbat, which is treated more stringently, the products of prohibited actions are permitted; is it not all the more so with regard to these prohibitions of plowing with an ox and a donkey and threshing with a muzzled animal, which are treated less stringently, that the products of prohibited actions should be permitted?
כלאי זרעים ליתסרו דהא תיעבתי לך הוא מדגלי רחמנא גבי כלאי הכרם (דברים כב, ט) פן תקדש פן תוקד אש מכלל דכלאי זרעים שרו The Gemara challenges: Diverse kinds of seeds sown together should be prohibited for consumption, as this is a matter whose practice I have made abominable to you. The Gemara explains: One learns otherwise from the fact that the Merciful One revealed with regard to diverse kinds in a vineyard: “You shall not sow your vineyard with two kinds of seed; lest the growth of the seed that you will sow be forfeited [pen tikdash]” (Deuteronomy 22:9). The Sages read the phrase “be forfeited [pen tikdash]” as though it states: Lest it be burned [pen tukad esh], indicating that diverse kinds in a vineyard must be destroyed so that no benefit is derived from them. Since this is stated specifically with regard to a vineyard, one can conclude by inference that other diverse kinds of seeds are permitted.
ואימא כלאי כרם אסורין בין באכילה בין בהנאה כלאי זרעים באכילה אסירי בהנאה שרו איתקוש לכלאי בהמה דכתיב (ויקרא יט, יט) בהמתך לא תרביע כלאים שדך לא תזרע כלאים מה בהמתך היוצא ממנה מותרת אף שדך היוצא ממנו מותר The Gemara objects: But say instead that the uniqueness of diverse kinds in a vineyard is that they are prohibited both for consumption and for benefit, whereas diverse kinds of seeds are prohibited for consumption but are permitted for benefit. The Gemara responds: One cannot say that diverse kinds of seeds are prohibited for consumption, as they are juxtaposed in the Torah to diverse kinds of animals, whose offspring are permitted. As it is written: “You shall not let your cattle mate with a diverse kind; you shall not sow your field with two kinds of seed” (Leviticus 19:19). The juxtaposition teaches that just as with regard to your cattle, the animal that comes from diverse species is permitted, so too, with regard to your field, that produce that comes from diverse seeds is permitted.
וכלאי בהמה גופייהו מנא לן מדאסר רחמנא כלאים לגבוה מכלל דלהדיוט שרי The Gemara asks: And with regard to diverse kinds of animals themselves, from where do we derive that their offspring is permitted? The Gemara answers: From the fact that the Merciful One prohibits the offspring of diverse kinds of animals for sacrifice to the Most High upon the altar (see 38b), learn by inference that they are permitted to ordinary people for consumption.
אותו ואת בנו ליתסר מדאסר רחמנא מחוסר זמן לגבוה מכלל דלהדיוט שרי The Gemara raises another difficulty: A mother and its offspring slaughtered on the same day should be prohibited for consumption, as this too is a practice made abominable. The Gemara answers: From the fact that the Merciful One prohibits an animal whose time has not yet arrived, i.e., that is less than eight days old, as an offering to the Most High (Leviticus 22:27), learn by inference that such animals are permitted to ordinary people for consumption. The offspring of a mother slaughtered that day is also considered an animal whose time has not yet arrived, since the prohibition against slaughtering it is limited to that day.
שילוח הקן ליתסר לא אמרה תורה שלח לתקלה The Gemara raises a final difficulty: If one violated the mitzva that mandates sending away the mother bird from the nest, as it is stated: “You shall not take the mother with the young. You shall in any way let the mother go” (Deuteronomy 22:6–7), and the court instructed him to set the mother bird free, that mother bird should be prohibited to all, as this practice is also abominable. The Gemara responds: The Torah did not say: Send it away, if doing so could lead to a mishap. If the bird were prohibited, the Torah would not have commanded one to send it away, as others might eat it unwittingly.
אמר ריש לקיש מנין לבשר בחלב שאסור ת"ל (שמות יב, ט) אל תאכלו ממנו נא ובשל מבושל שאין תלמוד לומר מבושל מה תלמוד לומר מבושל לומר לך יש לך בשול אחר שהוא כזה ואי זה זה בשר בחלב § Reish Lakish says: From where is it derived that meat cooked in milk is prohibited for consumption? The verse states with regard to the Paschal offering: “You shall not eat it partially roasted, nor boiled in any way” (Exodus 12:9). As there is no need for the verse to state: “Boiled in any way,” since it could simply have stated: “Boiled.” What is the meaning when the verse states: “Boiled in any way?” It is included to tell you that there is another manner of cooking, the product of which is prohibited like this one. And which cooking is this? This is meat cooked in milk.
א"ל רבי יוחנן Rabbi Yoḥanan said to Reish Lakish: