“Dreams are nothing other than a particular form of thinking, made possible by the conditions of the state of sleep. it is the dream-work which creates that form, and it alone is the essence of dreaming - the explanation of its peculiar nature.”

Source: Later Quote of Mondrian, about 1910-1914; in 'Mondrian, Essays' ('Plastic art and pure plastic art', 1937 and his other essays, (1941-1943) by Piet Mondrian; Wittenborn-Schultz Inc., New York, 1945, p. 10; as cited in De Stijl 1917-1931 - The Dutch Contribution to Modern Art, by H.L.C. Jaffé http://www.dbnl.org/tekst/jaff001stij01_01/jaff001stij01_01.pdf; J.M. Meulenhoff, Amsterdam 1956, p. 42

Reminiscences (1881), referring to his father, James Carlyle.
Sometimes quoted as "Man was created to work, not to speculate, or feel, or dream; Every idle moment is treason". The second of those two clauses in fact comes from Thomas Arnold The Christian Life (1841), Lecture VI.
1880s

Source: The Hero with a Thousand Faces (1949), Chapter 1
Context: Dream is personalized myth, myth is depersonalized dream; both myth and dream are symbolic in the same general way of the dynamics of the psyche. But in the dream the forms are quirked by the peculiar troubles of the dreamer, whereas in myth the problem and solutions shown are directly valid for all mankind.

Gott denkt in den Genies, träumt in den Dichtern und schläft in den übrigen Menschen.
Der Nachlass von Peter Altenberg, p. 20

"A Last Look at the Tube." New York Magazine, 17 March 1978, p. 45-48
1970s

A line written by Ono many years before, and quoted by Lennon in December 1980, as quoted in All We Are Saying : The Last Major Interview with John Lennon and Yoko Ono (2000) by John Lennon, Yōko Ono, David Sheff, p. 16.
Source: Grapefruit: A Book of Instructions and Drawings

Source: Les Misérables