"The line is from Gertrude Stein's poem Sacred Emily, written in 1913 and published in 1922, in Geography and Plays. The verbatim line is actually, 'Rose is a rose is a rose is a rose':
"Rose is a rose is a rose is a rose Loveliness extreme. Extra gaiters, Loveliness extreme. Sweetest ice-cream. Pages ages page ages page ages."