Negative commandment · Lo Ta’aseh #251 of 613
Not to hurt someone with words
שלא יונה בדברים
The verse · Vayikra 25:17
וְלֹא תוֹנוּ אִישׁ אֶת־עֲמִיתוֹ וְיָרֵאתָ מֵאֱלֹהֶיךָ כִּי אֲנִי ה׳ אֱלֹהֵיכֶם
“You shall not therefore defraud one another; but thou shalt fear thy God: for I am the Lord your God.”
The Rambam’s words
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.
שלא יונה בדברים, שנאמר "ולא תונו איש את עמיתו" (ויקרא כה, יז); זו אונאת דברים.
Why · Sefer HaChinuch #338
To not mistreat any Israelite with words
“The root of this commandment is well-known — for it is to give peace among the creatures. And great is peace, as through it is blessing found in the world; and difficult is disagreement — how many curses and how many tragedies are dependent upon it.”
Who & when
“And this commandment is practiced in all places and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Sales הלכות מכירה