“Students of the human mind have long noted its ability to mimic internally the positive notions and transformations of objects in the external world. In the middle of the eighteenth century, the British empiricist David Hume wrote that to "join incongruous shapes and appearances costs the imagination no more trouble than to conceive the most natural and familiar objects" and that "this creative power of the mind amounts to no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded us by the senses and experience."”

Part 1, Book 1, ch. 2, sect. 7.
Philosophy of the Inductive Sciences (1840)

Source: The Abbot's Ghost: A Christmas Story

Source: The Andromeda Strain

Quote in a letter of Dubuffet to Arnold Glimcher, as cited by Valery Oisteanu, Jean Dubuffet: The Last Two Years http://brooklynrail.org/2012/03/artseen/jean-dubuffet-the-last-two-years. The Brooklyn Rail, March 2012.
posthumous

Source: The Moral Judgment of the Child (1932), Ch. 2 : Adult Constraint and Moral Realism

As quoted in The 101 Habits of Highly Successful Screenwriters: Insiders Secrets from Hollywood's Top Writers (2001) by Karl Inglesias, p. 4. This has also appeared on the internet in several slightly paraphrased forms.
Context: The truly creative mind in any field is no more than this: a human creature born abnormally, inhumanly sensitive. To him, a touch is a blow, a sound is a noise, a misfortune is a tragedy, a joy is an ecstasy, a friend is a lover, a lover is a god, and failure is death. Add to this cruelly delicate organism the overpowering necessity to create, create, create — so that without the creating of music or poetry or books or buildings or something of meaning, his very breath is cut off from him. He must create, must pour out creation. By some strange, unknown, inward urgency he is not really alive unless he is creating.

Sermons, From Our Daily Bread

"Princeton In The Nation's Service" (21 October 1896)
1890s