The Nobel-winning physicist wrote to a New York businessman, Hyman Zinn, praising him for his work in helping Jewish refugees fleeing persecution in Hitler's Germany.
"It must be a source of deep gratification to you to be making so important a contribution toward rescuing our persecuted fellow-Jews from their calamitous peril and leading them toward a better future," he wrote.
The typed letter, with Einstein's embossed Princeton address, the original mailing envelope and described as in "very good to near fine condition," sold for $13,936 including buyer's premium, said LA auction house Nate D. Sanders.
The reserve price was between $5,000-7,000.
In the letter dated June 10, 1939 Einstein, who fled Germany for the United States when Adolf Hitler came to power in 1933, said Jews must help each other as they had for generations.
"The power of resistance which has enabled the Jewish people to survive for thousands of years has been based to a large extent on traditions of mutual helpfulness," said Einstein, the author of the theory of general relativity.
"In these years of affliction our readiness to help one another is being put to an especially severe test. May we stand this test as well as did our fathers before us."
And he wrote, "We have no other means of self-defense than our solidarity and our knowledge that the cause for which we are suffering is a momentous and sacred cause."
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