There cannot be a just cause for cursing a sinner if one be ignorant of his sentiments.
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic sentiment curse
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/18755/pg18755-images.html

Context

“"While the ungodly curseth the devil, he curseth his own soul." Much less therefore is it lawful to curse a man. Obj. 5: Further, a gloss on Num. 23:8, "How shall I curse whom God hath not cursed?" says: "There cannot be a just cause for cursing a sinner if one be ignorant of his sentiments." Now one man cannot know another man's sentiments, nor whether he is cursed by God. Therefore no man may lawfully curse another. On the contrary, It is written (Deut. 27:26) : "Cursed be he that abideth not in the words of this law."” source