Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 9
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 9, with English translation by Maimonides (Rambam).
שלא לעשות מעשה יידעוני, שנאמר "ואל היידעונים" (ויקרא יט,לא).
Not to perform the deeds associated with a yid'oni, as [Leviticus 19:31] states: "Do not turn to... the yid'onim."