“Fiery the Angels rose, and as they rose deep thunder roll'd
Around their shores: indignant burning with the fires of Orc.”

"Sacred Emily"
This statement, written in 1913 and first published in Geography and Plays, is thought to have originally been inspired by the work of the artist Sir Francis Rose; a painting of his was in her Paris drawing-room.
See also the Wikipedia article: Rose is a rose is a rose is a rose
Nigel Rees explains the phrase thus: "The poem 'Sacred Emily' by Gertrude Stein (1874-1946) is well-nigh impenetrable to the average reader but somehow it has managed to give a format phrase to the language. If something is incapable of explanation, one says, for example, 'a cloud is a cloud is a cloud.' What Stein wrote, however, is frequently misunderstood. She did not say 'A rose is a rose is a rose,' as she might well have done, but 'Rose is a rose is a rose is a rose' (i.e. no indefinite article at the start and three not two repetitions.) The Rose in question was not a flower but an allusion to the English painter, Sir Francis Rose, 'whom she and I regarded' wrote Constantine Fitzgibbon, 'as the peer of Matisse and Picasso, and whose paintings — or at least painting — hung in her Paris drawing-room while a Gauguin was relegated to the lavatory.'" - Sayings of the Century, page 91
Geography and Plays (1922)

Ring of Fire (1963); co-written with Merle Kilgore · June Carter Cash performance https://www.youtube.com/watch?v=nyNf6sw8xaE ·  Anita Carter version (1963) https://www.youtube.com/watch?v=OlWGsaorj6U · Johnny Cash performance (1987) https://www.youtube.com/watch?v=WEOdXU_JQPA ·  Johnny Cash performance (1994) https://www.youtube.com/watch?v=b-zNQA5Xi4Q ·  Live performance by June (1999) https://www.youtube.com/watch?v=tpRa6JbywTc

Source: Spirit Bound

A White Rose, lines 1-4, in In Bohemia (1886), p. 24.

Source: Rainer Maria Rilke - Sämtliche Werke (Complete Works)

Source: Spirit Bound

Source: Saffy's Angel

September Song http://www.poemhunter.com/poem/september-song/.
Poetry

The Rose that all are praising, reported in Bartlett's Familiar Quotations, 10th ed. (1919).