Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 192
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 192, with English translation by Maimonides (Rambam).
להתקין יד במחנה, שנאמר: "ויד תהיה לך, מחוץ למחנה" (דברים כג,יג).
To prepare a place [outside] the [army] camp [for use as a latrine], as [Deuteronomy 23:13] states: "Prepare a place for yourselves outside the camp."