The 233rd mitzvah is that a person is commanded to marry his female Jewish servant.1 Either her master or his son is commanded to marry her; and this is known as the mitzvah of yi'ud.

Our Sages said explicitly2 that "the mitzvah of yi'ud3 is preferable to the mitzvah of redemption," as seen from G‑d's statement4 (exalted be He), "if he does not perform yi'ud he must let her be redeemed."

You should be aware that the laws regarding both male and female Jewish servants apply only when the laws of the Jubilee Year are in effect.

The details of this mitzvah are explained in the first chapter of tractate Kiddushin.5