Sometimes it is used to grace webpages about anti-globalization politics, but you can also find it adorning discussions of theology. But it is almost invariably given without a source.
After a tenacious bit of googling, I think I may have found the source of it, and after a bit of time in Bobst library, I can now give it some context.
It would appear that the famous line attributed to Paul Éluard, is a détournement by Patrick White, who used it as an epigram to his novel The Solid Mandala (1966). By détournement, I mean a found line, not only copied and corrected, as the poet Lautréamont practiced it, and as the Situationists theorized it.
As you can see, the rabbit hole is still deeper. Éluard is here lifting a line from someone else, who is citing yet another.
This much I got from google. The above is thanks to the detective work summed up in a footnote in John Llewelyn, Margins of Religion, Indiana University Press, 2008, p. 452.
Llewelyn gives the source as Paul Éluard, Oeuvres completes, Galliamard, Paris, 1968, Vol. 1, p. 986.
The poet Picasso is referring to is, according to the notes, Swinburne.
This short piece is from a collection of Éluard prose pieces called Donner à voir of 1939.
Its curious that this much-détourned line is probably from a piece by Éluard that is arguably about a kind of détournement itself. Picasso and Éluard are interested in ways poets and painters might appropriate and correct from each other without citation or quotation. Each takes the work of the other as raw material.
And curious also that Éluard put this borrowed bit of text in between others that address the ‘spiritual’ but in a non-religious way, by Feuerbach and Poe.
So far so good: but this bit of detective work does not explain a détournement by EM Cioran: “There is no other world, not even this one.” Or by Octavio Paz: “There is another world, in this one.” So perhaps this isn’t the definitive explanation. But perhaps, in the internet age, those are becoming more elusive rather than less.