Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 256
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 256, with English translation by Maimonides (Rambam).
שלא לענות יתום ואלמנה, שנאמר "כָּל אַלְמָנָה וְיָתוֹם לֹא תְעַנּוּן" (שמות כב, כא).
Not to oppress any widow or orphan, as [Exodus 22:21] states: "Do not oppress any widow or orphan."