Nazir 62 - Willing slaves
A slave acquired by a Jew has to undergo circumcision and to accept on himself the majority of the mitzvot: he will be obligated too keep all the "don't do" prohibitions, but not all of the "do" commandments. Thus, his obligations are the same as a Jewish woman keeps.
What happens if a slave does not want to undergo circumcision or to accept the commandments? - The master is allowed to keep him for a year, to see if he changes his mind, but afterwards must sell him back.
Another uncommon feature of such slaves is that if the master, accidentally or on purpose, kicks out his tooth, eye, or finger - the slave goes to freedom. Once any slave acquires his freedom - he cannot be made slave again. In fact, he becomes a full Jew, with additional mitzvot of a Jewish man.
There is a difference between the laws of nazir for women and for slaves. For a woman, a husband can annul her vow, and in particular, a vow of becoming a nazir (nazirah). If they divorce or of the husband dies, the annulment is still active. However, with the slave it is not so. While the master can force the slave to drink wine and to go to a cemetery, this does not cancel the vow completely; when the slaves goes free, he needs to complete his term of nazir.
Art: Slaves on the West Coast of Africa by Francois-Auguste Biard