L’écrivain original n’est pas celui qui n’imite personne, mais celui que personne ne peut imiter. 
The Oxford Dictionary of Quotations (1979) 3rd edition 
Variant translations:
The original style is not the style which never borrows of any one, but that which no other person is capable of reproducing. 
As translated by Charles I. White (1856) Part 2, Book 1, Chapter 3 
An original writer is not one who imitates nobody, but one whom nobody can imitate. 
Bartlett's Familiar Quotations (1980) 15th edition. 
Le génie du Christianisme (1802)
                                    
“To refrain from imitation is the best revenge.”
Source: Meditations
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Marcus Aurelius 400
Emperor of Ancient Rome 121–180Related quotes
“Revenge is a dish best served unexpectedly and from a distance - like a thrown trifle.”
Source: Twilight Robbery
“Democracy is the best revenge.”
As quoted by her son, in "Democracy is the best revenge: Bilawal Bhutto Zardari," in Times of India (30 December 2007) http://web.archive.org/20080102174719/timesofindia.indiatimes.com/Democracy_is_best_revenge_Bilawal_Bhutto_Zardari/articleshow/2662912.cms?
“Living well is the best revenge.”
“520. Living well is the best revenge.”
Jacula Prudentum (1651)
“Revenge is a dish best eaten cold.”
                                        
                                        La vengeance est un plat qui se mange froid. 
Commonly said to be from Les liaisons dangereuses, but not found there. 
Misattributed