Letter of 1950, as quoted in The New York Times (29 March 1972) and The New York Post (28 November 1972). However, The New Quotable Einstein by Alice Calaprice (Princeton University Press, 2005: , p. 206, has a different and presumably more accurate version of this letter, which she dates to February 12, 1950 and describes as "a letter to a distraught father who had lost his young son and had asked Einstein for some comforting words":<blockquote>A human being is a part of the whole, called by us "Universe," a part limited in time and space. He experiences himself, his thoughts and feelings as something separate from the rest—a kind of optical delusion of his consciousness. The striving to free oneself from this delusion is the one issue of true religion. Not to nourish it but to try to overcome it is the way to reach the attainable measure of peace of mind.</blockquote> Letter transcript and photograph http://www.lettersofnote.com/2011/11/delusion.html
Google Translate, with its improved neural machine translation system, gives a slightly different translation of the original German quote, as discussed by Bryce Haymond on his blog https://thymindoman.com/2018/03/29/einsteins-misquote-on-the-illusion-of-feeling-separate-from-the-whole/.<blockquote>A human being is a spatially and temporally limited piece of the whole, what we call the “Universe.” He experiences himself and his feelings as separate from the rest, an optical illusion of his consciousness. The quest for liberation from this bondage is the only object of true religion. Not nurturing the illusion but only overcoming it gives us the attainable measure of inner peace.</blockquote>
Kontext: A human being is a part of the whole, called by us "Universe", a part limited in time and space. He experiences himself, his thoughts and feelings as something separated from the rest — a kind of optical delusion of his consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest to us. Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty. Nobody is able to achieve this completely, but the striving for such achievement is in itself a part of the liberation and a foundation for inner security.