Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos) By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
Second Section – the Negative Commandments
48. It is a negative commandment “Do not hurt one’s friend with words.”
As it states in Vayikra (Leviticus) 25:17, “and a man shall not wrong another.” This means, a person should not say to a person who repented from his previously sins, “remember your old ways.” Nor should he say to a convert, “remember the ways of your father.” Nor should he ask a matter of wisdom from one who does not have wisdom, thereby hurting him. Anything like this is wronging with words.
4. Be kind to yourself. Speaking badly even about yourself is unethical.
הלכות שמירת הלשון 