Back to Methuselah pt. 1, act 1 (1921). This was a favorite quotation of Robert F. Kennedy's, and Edward M. Kennedy used it in his eulogy of Robert Kennedy.
"Edith Sitwell, a Unicorn Among Lions". Book by Victoria Glendinning (p. 54), 1981; later quoted in "An Uncommon Scold" edited by Abby Adams (p. 74), November 1, 1989.