Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 18
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 18, with English translation by Maimonides (Rambam).
שלא לעזוב השנאה למסית, שנאמר "ולא תשמע אליו" (דברים יג,ט).
Not to reduce one's hatred for a mesit, as [Deuteronomy 13:9] states: "Do not listen to him."