Gemara

R. Meir permits an animal slaughtered on Shabbos only when one (in the household) was (dangerously) sick when Shabbos began. (They planned to slaughter for him if necessary.)

Question: If so, it was permitted to slaughter. Why does R. Yehudah forbid the meat?

Answer: The case is, he became Bari (healthy) again before the Shechitah; like Rav Acha taught.

(Rav Acha bar Rav Ada bar Ahavah citing Rav): If one slaughters (on Shabbos) for a Choleh (sick person), a Bari may not eat from the meat. If one cooks for a Choleh, a Bari may eat the food.

This is because one could not eat the meat without Shechitah, but food could have been eaten raw.

(Rav Papa): Sometimes one slaughters for a Choleh and a Bari may eat from the meat, e.g. someone was sick when Shabbos began;

Sometimes one cooks for a Choleh and a Bari may not eat the food, e.g. he cut gourds.

(Rav Dimi of Nehardai): The Halachah is, if one slaughters for a Choleh, a Bari may eat from the meat raw.

Since one must slaughter to eat even a k'Zayis, there is no concern lest he slaughters also for the sake of a Bari.

If one cooks for a Choleh, a Bari may not eat the food.

This is a decree, lest he come to cook extra for a Bari.

Beitzah 24b (Rav Papa): The Halachah is, if a Nochri brought Peros on Yom Tov, if there are attached Peros of that species, we forbid the Peros until the time to pick them after Yom Tov.

37b (Rav): If partners (in different Techumim) bought a flask of wine and an animal together, they may divide the wine (on Yom Tov), but not the animal.

He holds that Yesh Breirah (it is as if from the beginning, each bought the half that he will receive when they divide). He forbids the animal because each half nurtures from the other half in a different Techum.

Question (Rav Kahana and Rav Asi): If you are not concerned for Muktzeh, you should not be concerned for Techumim!

Rishonim

Rif and Rosh (Chulin 4a and 1:20): The Halachah is, if one slaughters for a Choleh, a Bari may eat from the meat raw. If one cooks for a Choleh, a Bari may not eat the food. This is a decree, lest he come to cook extra for healthy people.

Rambam (Hilchos Shabbos 2:9): If one cooked for a Choleh on Shabbos, and he ate and food was leftover, a Bari may not eat from the leftovers. This is a decree lest they cook extra for a Bari. If one slaughtered on Shabbos for a Choleh, one (a Bari) may eat the meat raw.

Beis Yosef (DH v'Im): The Rosh, Magid Mishneh and R. Yonah say that an animal slaughtered on Shabbos is not Muktzeh, for we hold like R. Shimon, who forbids Muktzah due to Isur only if one was Docheh b'Yadayim (did an act that prevents him from using it). Why are living animals different than attached Peros? They are forbidden, because he did not detach them from before Shabbos. I wanted to say that they explain that we forbid Peros that a Nochri brought on Yom Tov not due to Muktzeh. Rather, it is lest one detach. Even if it is due to Muktzeh, we can say that this is like R. Yehudah. The Rif and Rambam rule like R. Yehudah regarding Yom Tov, but like R. Shimon regarding Shabbos. However, the Rosh says that it is because he did not detach them from before Shabbos. Perhaps he holds that anyone can detach Peros, but not everyone can slaughter and it is a big toil. Perhaps he wanted to slaughter, but he did not find an expert Shochet or checked knife or time to slaughter. Therefore, there is no proof that he diverted his mind from it. Alternatively, the Rosh holds like the opinion that R. Shimon permits even animals that died on Shabbos. This shows that they are not Muktzeh.

Tosfos (Beitzah 37b DH l'Isur): What Isur Muktzeh applies to the animal? The Rashbam explains that it grows fatter on Yom Tov. Even though Rav holds like R. Yehudah, who forbids Muktzeh, he was not concerned for this. If so, he should not be concerned for nurturing and growing from the half in the other Techum!

Poskim

Shulchan Aruch (OC 318:2): If one slaughtered on Shabbos for a Choleh, whether he was sick from before Shabbos, or he fell sick on Shabbos, a Bari may eat it raw (on Shabbos).

Magen Avraham (4): The Rosh permits because we hold like R. Shimon, who forbids Muktzeh only if one was Docheh b'Yadayim. If so, we should permit also attached Peros that fell! We can say that we are stringent about Peros, lest one detach them.

Kaf ha'Chayim (23): We are not concerned lest one slaughter, for it is a burden, and he will remember that it is forbidden. Also, we decree only about Peros, which one can eat while they are in his hands, and he craves them.

Mishnah Berurah (10): A Bari may eat the meat raw, but he may not salt it on Shabbos. It must be rinsed due to intact blood (on the surface). There is no Isur of blood absorbed (in the limbs) that never separated.

Shulchan Aruch (ibid.): However, if one cooked (or did another Melachah) for a col on Shabbos, it is forbidden (on Shabbos) for a Bari or a Choleh without danger, lest people do extra (Melachah) for the Bari.

Gra (DH Oh): Regarding Melachah of a Yisrael, a Choleh without danger is like a Bari in every way.

Kaf ha'Chayim (29): (Even though one may tell a Nochri to cook for a Choleh without danger), we decree to forbid anything that one may not do through a Yisrael, lest they not find a Nochri, and a Yisrael will do extra (for the Choleh).

Magen Avraham (6): Some say that the Isur to add is mid'Oraisa, even if he adds before putting the pot on the fire. Some say that it is mid'Rabanan.

Mishnah Berurah (13): In my Sefer Ahavas Chesed I proved from the Gemara that the first opinion is primary.

Kaf ha'Chayim (30): This affects a Choleh without danger. One may transgress mid'Rabanan Isurim for him, but not mid'Oraisa.

Gra: Eruvin 68a teaches that one may cook extra through a Nochri only for the sake of Bris Milah.

Kaf ha'Chayim (28): If the food was edible raw, anyone may move it. If not, others may move it only for the sake of the Choleh.

Rema: Even if he cooked through a Nochri, it is forbidden on Shabbos.

Magen Avraham (7): It is permitted immediately on Motza'ei Shabbos. Since the Nochri cooked b'Heter, one need not wait after Shabbos the time to cook.

Kaf ha'Chayim (31): The Rema (YD 113:16, citing the Ro'oh) and Shach (YD 123:50) add that there is no Isur of Bishul Akum (Chachamim decreed against food cooked by Nochrim), since it was permitted for him to cook for the Choleh. However, the Taz (YD 113:15) brings from the Rashba that even the Choleh may not eat it after Shabbos,). He was permitted only when it was necessary (on Shabbos, Yisre'elim could not cook for him). Many say that since the Mechaber did not bring the Ro'oh's reasoning, he forbids. If it is a food to which Bishul Akum never applies, it is permitted immediately after Shabbos.

Mishnah Berurah (11): On Shabbos one may taste the food while cooking it.

Rema: If one detached fruits on Shabbos for a Choleh, even if he was sick from before Shabbos, it is forbidden to a Bari on Shabbos, for it constantly grows on Shabbos, so it is Muktzeh.

Magen Avraham (8): This discusses Peros that were not fully ripe. If they were fully ripe, we do not forbid because they keep growing. If we would not say so, why did the Gemara need to forbid attached Peros lest one detach them, or due to Muktzeh? Rather, those reasons are needed for when the Peros were fully ripe. Tosfos (Bava Kama 69a DH Kol) says that the additional growth is Batel in the majority. Tosfos (Beitzah 37b) connotes that this is not Muktzeh even according to R. Yehudah, for also an animal constantly grows, and one may slaughter it on Yom Tov.

Gra: The Rema learns from Chulin. We forbid a gourd detached on Shabbos, even if the Choleh was sick from before Shabbos, like Shechitah, which was taught with it. This is unlike Rashi (15b DH veha'Mevashel), who permits what was detached for one who was sick from before Shabbos.

Gra (DH Mishum): Regarding an animal, we are not concerned for the fact that it keeps growing. See Tosfos Beitzah 37b.

Mishnah Berurah (15): Even if from before Shabbos he intended to detach it on Shabbos, it is forbidden. Preparation does not help for something attached, since it grows on Shabbos. However, if it was fully ripe and does not grow more, preparation helps even though it is attached. If the Choleh became sick today, in any case a Bari may not benefit from it, for it is Muktzeh.

Mishnah Berurah (16): The Magen Avraham asked that the added growth should be Batel to the majority. Also the Gra leans to say so l'Halachah.

Kaf ha'Chayim (35): One must wait after Shabbos the time to do a Melachah (that was done for a Choleh), but not if the Isur was due only to Muktzeh or a decree lest people do extra.