Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 251
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 251, with English translation by Maimonides (Rambam).
שלא יונה בדברים, שנאמר "ולא תונו איש את עמיתו" (ויקרא כה, יז); זו אונאת דברים.
Not to hurt someone with words, as [Leviticus 25:17] states: "And one man shall not wrong another." This [prohibition refers to] hurting someone with words.