Gemara

47b (Beraisa - R. Shimon ben Elazar): If a man captured a Yafes To'ar (a beautiful Nochris) in war, even if she did not accept (to convert), he may immerse her to become a slave, and immerse her a second time to free (convert) her.

(Rava): He learns from "Kol Eved Ish (... you will circumcise him)". Surely this applies also to the slave of a woman! Rather, you may circumcise Eved Ish (a male slave) against his will, but not Ben Ish (a Nochri) against his will.

(Ula): Chachamim say that just like you cannot circumcise a Nochri against his will, you cannot circumcise a slave against his will. They use "Eved Ish" to teach Shmuel's law, that one is a slave only if he has a master; a Hefker slave does not need a Get Shichrur.

Objection (Rav Papa): Chachamim's law applies only to a Yafes To'ar, since she is not yet commanded in Mitzvos. A slave is already commanded in Mitzvos, so Chachamim would agree that one may circumcise him against his will!

(Beraisa): The law of a slave bought from a Nochri is like the law of a convert: he must accept the Mitzvos.

Inference: A slave bought from a Yisrael need not accept the Mitzvos!

Question: A Beraisa (47b) equates a freed slave to a convert (he must accept)!

Answer: He is equated regarding Tevilah (but a freed slave need not accept).

48b (Beraisa - R. Yishmael): One may keep slaves who refuse to be circumcised;

R. Akiva forbids.

R. Yishmael: But it says "The son of your slave will rest"!

R. Akiva: That refers to one who bought a slave Bein ha'Shemashos (when Shabbos was entering) and did not have time to circumcise him.

Question: All agree that the verse discusses an Arel (uncircumcised) slave. How do they know this?

Answer (Beraisa): "Your male and female slave will rest like yourself" teaches about circumcised slaves, so "the son of your slave..." refers to an Arel slave.

"The Ger in your gates" teaches about converts, so "(the son of your slave will rest) veha'Ger" refers to a Ger Toshav (a Nochri who keeps his seven Mitzvos).

(R. Yehoshua ben Levi): If a slave bought from a Nochri refuses to be circumcised, one may keep him for 12 months. If he still refuses, he must be sold to a Nochri.

Rabanan: This is unlike R. Akiva, who forbids keeping him!

Rav Papa: It is even like R. Akiva. We distinguish between whether or not he was Posek the matter (this will be explained).

Question (Rav Zvid): If so, R. Akiva did not need to say that the verse discusses a slave bought Bein ha'Shemashos! (He could say that it is when he was Posek!)

Answer: He gave one of two possible answers.

(Ravin): One may keep an Arel slave only if he bought him intending not to circumcise him.

Rabanan: This is unlike R. Akiva, who forbids keeping him!

Rav Papa: It may be even like R. Akiva. R. Akiva forbids when he did not stipulate (that he will remain Arel). If he stipulated, it is permitted.

Question (Rav Zvid): If so, why did R. Akiva say that the verse discusses a slave bought Bein ha'Shemashos? He could have said that it is when he stipulated!

Counter-question: How do you explain why he didn't say that it discusses a slave when he was Posek!

Answer to both questions: We must say that R. Akiva gave one of two or three possible answers.

Rishonim

Rif: Rav Papa concludes that a freed slave need not accept the Mitzvos, because he accepted before (when he became a slave). A Beraisa requires a slave bought from a Nochri to accept, i.e. but a slave bought from a Yisrael need not.

Rambam (Hilchos Milah 1:6): If one bought an adult slave from Nochrim and he did not want to be circumcised, one may keep him Arel for 12 months, but no longer. Rather, he sells him back to Nochrim. If when he still belonged to his Nochri master he stipulated that he will not circumcise, one may keep him Arel, as long as he accepts the seven Mitzvos of Benei No'ach. He will be like a Ger Toshav. If he does not accept the seven Mitzvos he is killed immediately. We accept a Ger Toshav only when Yovel applies.

Rambam (Hilchos Isurei Bi'ah 14:9): When one buys a slave from Nochrim, we do not ask him 'why do you want (to be part of Yisrael)'. Rather, we ask him whether or not he wants to be a slave of Yisrael, i.e. to be a Kosher person. If he wants, we tell him the primary tenets of Torah, some light and some severe Mitzvos, and their punishment and reward, like we tell to a convert. We immerse him like a convert, and we inform him while he is in the water. If he did not want to accept, one keeps him for 12 months but no longer, and then sells him to Nochrim. If he stipulated from the beginning that he will not circumcise or immerse, rather he will be a Ger Toshav, one may keep him for a Ger Toshav slave. We may keep such a slave only when Yovel applies.

Ra'avad (8): Certain laws of a Ger Toshav depend on Yovel, i.e. dwelling in the city with Yisraelim and the Mitzvah to support him. If a slave stipulated not to be circumcised one may keep him as long as desired, even when Yovel does not apply.

Rosh (4:38): R. Akiva holds that since Hash-m commanded Avraham to circumcise his slaves, it is forbidden to keep Arel slaves. Therefore, if he stipulated it is permitted, for the verse discusses only Stam slaves. "The son of your slave will rest" refers to an Arel slave, e.g. one bought a Shifchah and her adult son. We learned about circumcised slaves from "In order that your male slave and female slave will rest like yourself". Rashi (Yevamos 48b DH Ger) explains that a Ger Toshav is one who accepted not to serve idolatry. The verse commands him about Shabbos. This is difficult. Shabbos is not one of the seven Mitzvos of a Ger Toshav (Avodah Zarah 64b)! If a Ben No'ach desists from Melachah on any day he is Chayav Misah (Sanhedrin 58b)! Kerisus 9b also connotes that a Ger Toshav need not keep Shabbos. Rather, the verse refers to a Ger Toshav who works for a Yisrael and was raised in his house.

Rosh (ibid.): Rashi (Yevamos 48b DH Aval) explains that 'he was Posek' means that when he was bought he agreed to convert, but later retracted. Alternatively, he allotted 12 months, by which time he must be circumcised.

Ran (Gitin 23a DH Sholach): Every day we give him a taste of Divrei Torah to draw him under the wings of the Shechinah.

Rosh (ibid.): Rav Hai Gaon says that it means that the slave refuses to be circumcised. There is no Mitzvah to circumcise him, so one may keep him for 12 months; perhaps he will agree. If he agrees to be circumcised but keeps stalling one may not keep him, for we do not delay Mitzvos.

Nimukei Yosef (DH Tanu): R. Chananel says that 'he was Posek' means that the slave said that he will not convert. One may not keep him (at all).

Question: Why do we need his consent? One can immerse a slave to become an Eved Kena'ani against his will!

Answer #1 (Nimukei Yosef DH Tanu): The case is, the slave said that if he is immersed he will not keep Mitzvos, and the master sees that he is stubborn.

Answer #2 (Rosh): It is an enactment mid'Rabanan not to do so, lest a slave who did not want to accept Mitzvos cause his master to transgress. Also, it is not good to make him obligated in Mitzvos if he does not want to observe them. R. Yehoshua ben Levi holds that making a slave Hefker does not free him (Gitin 39b). He must expound "Kol Eved Ish" to teach that one can immerse a slave b'Al Korcho, nevertheless he allows keeping an Arel slave only 12 months. Also R. Shimon ben Elazar expounds this way, yet he does not allow keeping Arel slaves in Eretz Yisrael! We must say that there was a decree mid'Rabanan not to immerse b'Al Korcho. This is according to Rashi, who says that Chachamim argue only about immersion for conversion b'Al Korcho, but all agree that one may immerse a slave b'Al Korcho. It seems that the Rif requires consent also for immersion to become an Eved Kena'ani.

Magid Mishneh (Isurei Bi'ah 14:8): The Rambam holds like the Rif.

Poskim

Shulchan Aruch (YD 267:4): If one bought an adult slave from Nochrim and he did not want to be circumcised, one may keep him for 12 months. One may not keep him longer when he is Arel. Rather, he sells him back to Nochrim.

Shach (9): The Ri says that the Isur is mid'Oraisa. The Rivan says that it is mid'Rabanan.

Rema: This is only if he bought him to convert him to be a slave. If he explicitly stipulated not to circumcise him, one may keep him as long as he wants. In our lands where it is forbidden to convert any Nochri, it is as if he stipulated not to circumcise him. This is the custom.

Beis Yosef (DH veha'Rambam): The Tur omitted the Heter to keep a slave who stipulated not to circumcise because it is permitted only if he will be a Ger Toshav, which applies only when there is Yovel.

Drishah (2): The Beis Yosef's text of the Tur did not bring this Heter. Our text of the Tur does. The Tur rules that Ger Toshav applies nowadays, like the Ra'avad.

Shach (10): It is never a problem to rent a Nochri worker if he is not acquired permanently to be a slave.