Marcus Tullius Cicero, Pliny (2010). “Letters of Marcus Tullius Cicero with His Treatises on Friendship and Old Age: Letters of Pliny the Younger”, p.13, Cosimo, Inc.
Marcus Tullius Cicero (1856). “Cicero's Three Books Of Offices, Or Moral Duties: Also His Cato Major, an Essay on Old Age; Laelius, an Essay on Friendship; Paradoxes; Scipio's Dream; and Letter to Quintus on the Duties of a Magistrate”, p.186