What do scriptures say about using swear or abusive words for cursing people?
Vidura discusses the importance of controlling one's speech
To control speech, O king, is said to be most difficult. It is not easy to hold a long conversation uttering words full of meaning and delightful to hearers. Well-spoken speech is productive of many beneficial results; and ill-spoken speech, O king, is the cause of evils. A forest pierced by arrows, or cut down by hatchets may again grow, but one’s heart wounded and censured by ill-spoken words never recovereth. Weapons, such as arrows, bullets, and bearded darts, can be easily extracted from the body, but a wordy dagger plunged deep into the heart is incapable of being taken out. Wordy arrows are shot from the mouth; smitten by them one grieveth day or night. A learned man should not discharge such arrows, for do they not touch the very vitals of others.
[Mahabharata, Udyoga Parva, Section 34]
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