“Forgive your enemies, but don’t forget their names”

“Forgive your enemies, but don’t/never forget their names” (or “Forgive your enemies, but always remember their names”) is a quotation attributed to both John F. Kennedy (1917-1963) and Robert F. Kennedy (1925-1968). The earliest known citation of the quotation, however, appears to be 1981.
 
   
Wikiquote: Enemies
Unsourced
Forgive your enemies, but never forget their names.
John F. Kennedy
 
Google Books
The Yale Book of Quotations
Edited by Fred R. Shapiro
New Haven, CT: Yale University Press
2006
Pg. 423:
Robert F. Kennedy
U.S. politician, 1925-1968
“Always forgive your enemies—but never forget their names.”
Quoted in Nancy McPhee, The Second Book of Insults (1981)
     
Google Books
6 May 1981, Ellensburg (WA) Daily Record, “A little land, lots of water” by Louis M. Boyd, pg. 22, col. 1:
Was none other than president John F. Kennedy who said: “Forgive your enemies, but never forget their names.”
 
Google News Archive
17 September 1983, Kentucky New Era (Hopkinsville, KY), pg. 4, col. 5:
As John F. Kennedy said, “Forgive your enemies, but don’t forget their names.”
 
Google Books
Mayor
By Ed Koch with William Rauch
New York, NY: Simon and Schuster
1984
Pg. 98:
I remembered what his brother Jack had said: “Forgive your enemies, but never forget their names,” and I quoted it to him.
 
Google Books
Portrait in Oil
By Charles Fox
Garden City, NY: Doubleday
1984
Pg. 288:
“I figured they’d know the rule: forgive your enemies but don’t forget their names.”
     
Forbes.com
On the Business of Life
10.18.99
(...)
Forgive your enemies, but never forget their names. -JOHN F. KENNEDY