Known sourcecanonical
"Treason doth never prosper: what 's the reason? Why, if it prosper, none dare call it treason."
Sir John Harrington / Epigrams. Book iv. Ep. 5.
Epigrams. Book iv. Ep. 5.
Bartlett's Familiar Quotations, 9th ed. (Little, Brown, 1905), public domain