Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 264
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 264, with English translation by Maimonides (Rambam).
שלא לכבוש אשת יפת תואר שפחה, שנאמר "לֹא תִתְעַמֵּר בָּהּ" (דברים כא, יד).
Not to force a yefat to'ar to serve as a maidservant, as [Deuteronomy, ibid.] continues: "Do not rule over her."