"Epistolæ Ad Lucilium" by Marcus Fabius Quintilianus as reported in "Hoyt's New Cyclopedia Of Practical Quotations" by Jehiel Keeler Hoyt, p. 878-82., 1922.
"On the Happy Life". Essay by Seneca the Younger (58 AD); later published in Sir Edward Bulwer-Lytton "Caxtoniana: A Series of Essays on Life, Literature, and Manners", p. 174 (in the essay "The Sympathetic Temperment"), 1863.