Source, in full
Drawing is the probity of art. To draw does not mean simply to reproduce contours; drawing does not consist merely of line: drawing is also expression, the inner form, the plane, modeling. See what remains after that. Drawing includes three and a half quarters of the content of painting. If I were asked to put up a sign over my door, I should inscribe it: School for Drawing, and I am sure that I should bring forth painters.
Notes from Wikiquote
«Du dessin», in Pensèes d’Ingres (Paris: Sirène, 1922), p. 70; translated by Walter Peach, Ingres (New York: Harper & Bros., 1939), p. 170