For nothing is more commendable, nothing more becoming in a pre-eminently great man than courtesy and forbearance.
 Marcus Tullius Cicero, On Duties (44 BC). copy citation

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Author Marcus Tullius Cicero
Source On Duties
Topic courtesy
Date 44 BC
Language English
Reference
Note Translated by Walter Miller
Weblink http://www.constitution.org/rom/de_officiis.htm

Context

“there was in it no trace of rancour. {88} Neither must we listen to those who think that one should indulge in violent anger against one's political enemies and imagine that such is the attitude of a great-spirited, brave man. For nothing is more commendable, nothing more becoming in a pre-eminently great man than courtesy and forbearance. Indeed, in a free people, where all enjoy equal rights before the law, we must school ourselves to affability and what is called "mental poise";/a for if we are irritated when people intrude upon us at unseasonable hours or make unreasonable requests, we shall develop a sour, churlish temper, prejudicial to ourselves and offensive to others.” source