source
Empedocles (c. 460 BC) as quoted by Sir Thomas Little Heath, A History of Greek Mathematics, [https://books.google.com/books?id=h4JsAAAAMAAJ Vol. 1], p.65, citing Diog. L. viii. 54 and Porph. V. Pyth. 30 (Fr. 129 in Vorsokratiker i3, p. 272. 15-20).