"The Golden Sayings of Epictetus" by Epictetus, translated by Hastings Crossley, Vol. II, Part 2, The Harvard Classics. New York: P.F. Collier & Son, 1909.
Marshall B. Rosenberg (2004). “Teaching Children Compassionately: How Students and Teachers Can Succeed with Mutual Understanding”, p.31, PuddleDancer Press