Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 317
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 317, with English translation by Maimonides (Rambam).
שלא לקלל אחד משאר ישראל, שנאמר "לא תקלל חירש" (ויקרא יט,יד).
Not to curse any other Jew, as [Leviticus 19:14] states: "Do not curse [even] a deaf-mute."