Gemara

(Rav Acha bar Papa): If one who buys a house in Eretz Yisrael, the document of sale may be written on Shabbos.

Objection: This cannot be!

Answer: We tell a Nochri to write the document. Normally, Amirah l'Nochri (asking him to do what is forbidden to Yisrael) is Shevus (forbidden mid'Rabanan). Here, Chachamim did not decree, to promote settling Eretz Yisrael.

Bava Metzia 10b (Ravina): Ein Shali'ach l'Devar Aveirah only when the Shali'ach is Bar Chiyuva (liable for transgressing).

(Rav Sama): Ein Shali'ach l'Devar Aveirah only when the Shali'ach can choose whether or not to comply.

90a - Question: May Reuven tell a Nochri 'muzzle my cow and thresh with it'?

Amirah l'Nochri is forbidden. Is this a stringency of Shabbos (since one who desecrates Shabbos is liable to death), but it does not apply to muzzling, which is only a Lav? Or, is there no distinction!

Answer - Question (from Eretz Yisrael): If Nochrim steal bulls from Yisraelim, castrate them and return them, what is the law?

Answer (Shmuel's father): This is a ruse. We force the owners to sell them. (Even though castration is only a Lav, one may not ask a Nochri to do it.)

Rejection (Rav Papa): In Eretz Yisrael, they hold like Rav Chidka, who forbids Nochrim to castrate. A Yisrael may not ask them to do so, due to "Lifnei Iver."

Rishonim

The Rif (Bava Metzia 52b) brings the Sugya on 90a.

Rambam (Hilchos Shabbos 6:21): If a Nochri brought his things into Levi's house on Shabbos it is permitted, even if Levi said 'leave them in this corner.'

Magid Mishneh: We totally permit Amirah l'Nochri about his Melachah. Even if his things are Muktzah, one may tell him where to put them.

Rosh (7:15): Amirah l'Nochri is forbidden on Shabbos. We permit only to promote settling Eretz Yisrael, but not for other Mitzvos like Bris Milah (Eruvin 68a).

Rosh (Bava Metzia 7:6): One may tell a Nochri to eat a Neveilah, for a Yisrael may put a Neveilah in a Nochri's mouth, like he commands the Nochri. The Gemara asked about when a Yisrael may not do what he commands the Nochri, e.g. muzzling. Similarly, one may not tell a Nochri 'cook this meat for yourself on Shabbos', even if he need not feed the Nochri. Rav Sadya Gaon learns from our Gemara that even before Shabbos, one may not give money to a Nochri and tell him to buy a certain item. Even though the Nochri will not thresh immediately, if one were Chayav Misah for muzzling, it would be forbidden to tell a Nochri to do so. I challenge his proof, for here he commands at a time when the Isur applies.

Pilpulei Charifta (9): Even though buying is forbidden only mid'Rabanan, it involves a Chiyuv Misah, i.e. transferring from one Reshus to another.

Nimukei Yosef: If Levi has his wallet in Reshus ha'Rabim just before Shabbos, we are lenient to let him give it to a Nochri (to take to Levi's home), for a person is frantic about his money. The Ran proves from here that even before Shabbos one may not tell a Nochri to do Melachah on Shabbos.

Rashi (71b DH Bishlomo): Mid'Rabanan, we are stringent to say that a Nochri can be a Yisrael's Shali'ach.

Poskim

Shulchan Aruch (OC 307:21): On Shabbos, one may not tell a Nochri 'cook this meat for yourself', even if he need not feed the Nochri.

Beis Yosef (DH Kosav b'Hagahos): The Mordechai (Shabbos 459) permits telling a Nochri 'do your Melachah' on Shabbos. The Rosh forbids.

Mishnah Berurah (73): Since the Yisrael may not do so, we forbid Amirah l'Nochri, even though the Yisrael gets no benefit. Chachamim did not forbid if the meat never belonged to the Yisrael and the Nochri acts for himself.

Mishnah Berurah (74): One may not tell the Nochri even before Shabbos.

Kaf ha'Chayim (136): Since he tells the Nochri to do so, this shows that he wants him to do so, so he is like his Shali'ach.

Rema: One may tell him to do Melachah for himself.

Kaf ha'Chayim (138): A doctor may tell a Nochri what to do with his own medicine. If the Yisrael's oil is needed, he should sell it to him before Shabbos.

Kaf ha'Chayim (141): If Levi hired a Nochri to do a Melachah for a fixed wage, on Shabbos David may tell the Nochri to do it.

Kaf ha'Chayim (143): Levi may tell a Nochri to move Levi's Kli she'Melachto l'Isur to avoid loss of the Kli, for if Levi needed the Kli, he could move it.

Kaf ha'Chayim (144): One may tell the Nochri to do Melachah with his own things even if the Yisrael will benefit, e.g. 'extinguish your fire', so the Yisrael's property will not burn.

Question (Teshuvas Pnei Yehoshua EH 3): According to those who are stringent to say that Yesh Shelichus l'Nochri, why was the Gemara unsure about Amirah l'Nochri for a Lav? Since Yesh Shelichus l'Nochri, it is as if the Yisrael does it! Rav Sama says Ein Shali'ach whenever the Shali'ach can choose whether or not to do it. Ravina says Yesh Shali'ach whenever the Shali'ach is not Bar Chiyuva. How can he answer? Perhaps we asked according to Rav Sama. However, throughout Shas we say that Amirah l'Nochri is Shevus. According to Ravina, it is mid'Oraisa, for Yesh Shali'ach!

Answer (Beis Meir 14): Ein Shali'ach does not apply to Amirah l'Nochri. It is only when Hash-m despises an action, e.g. castration or muzzling, even when Nochrim do so. Tosfos (Chulin 115a DH Kol) asked why 'all that Hash-m called abominable' does not forbid an animal castrated by Nochrim. He answered that since the Torah forbids to the Mizbe'ach, we infer that it is permitted to people. Therefore, Shali'ach l'Devar Aveirah applies. It is a Mitzvah for a Yisrael and his (property) to rest on Shabbos. Melachah is not an intrinsic Aveirah. The Torah allows putting a pot next to a fire before Shabbos, so it will cook on Shabbos. A Nochri who observes Shabbos is Chayav Misah! Shali'ach l'Devar Aveirah does not apply, for the Yisrael rests. Shelichus does not apply even to some Mitzvos Aseh, e.g. to wearing Tefilin.

Question (Beis Meir): One may not make Havdalah on a lamp lit on Shabbos, even if a Nochri lit it, for it did not cease from forbidden Melachah (Berachos 53a, Shulchan Aruch OC 298:5). Perhaps it is merely a trace of an Aveirah. However, Rashi (Shabbos 153a DH Mai) says that Shelichus applies to a Nochri on Shabbos. He must refer to the Shevus of Amirah l'Nochri. Also the Ran (cited in Nimukei Yosef) forbids due to Shelichus, for he holds that Amirah l'Nochri is only regarding Shabbos. Rashi need not hold like Ravina. He can say that just like Ein Shelichus l'Nochri, but l'Chumra Yesh Shelichus, just like l'Chumra a Nochri can be a Shali'ach l'Aveirah.

Chasam Sofer (OC 84): The Pnei Yehoshua (YD 3) asked that according to the opinion that Yesh Shelichus l'Nochri l'Chumra, why did the Gemara (Bava Metzia 90a) ask about telling a Nochri to castrate or muzzle animals? Yesh Shali'ach l'Devar Aveirah, since the Nochri is not Bar Chiyuva! We must say that the Sugya is like the opinion that Yesh Shali'ach only when the Shali'ach has no choice. The Rambam forbids Ribis through a Nochri mid'Oraisa, and obligates returning it. He holds that Chachamim forbade any Isur done through a Nochri even b'Di'eved, e.g. cooking on Shabbos or castration. (Those who disagree say that Chachamim were more stringent about Shabbos and scheming, i.e. castration). The Rambam does not hold that Yesh Shelichus l'Nochri mid'Oraisa. Maharshach says that even though Yesh Shelichus l'Nochri, Chachamim stressed Amirah l'Nochri. It is more severe, for the Yisrael transgresses "v'Daber Davar (discussing Melachah)." This is reasonable only if Shelichus l'Nochri is also mid'Rabanan. Alternatively, he holds that it is mid'Oraisa, except for Shabbos. Similarly, bowing to idolatry is an action with one's body, and Shelichus does not apply to it.