The Buddha's Teachings on Guarding Against Harsh Words

Dhammapada, Chapter 10 (Punishment), Verse 133
"Do not recklessly utter harsh and ferocious words toward others.
The coarse words you carelessly cast out will soon return to you
as even greater calamity and suffering.
A tool used to wound others is like a sharp blade
that cuts one's own soul. Among all the languages of the world,
insults and fierce speech born of anger are like a raging fire
that consumes the body; they turn not only the listener's heart,
but the heart of the speaker into nothing but ashes.
Therefore, the wise person always plants the seeds of speech with caution,
preventing the terrible disasters that stem from the tip of the tongue
and reflecting upon their own life."