"Refutation of all heresies, Book IX (Fragment 52)". Book by Hippolytus of Rome (3rd century AD), as later translated in Carl Avren Levenson and Jonathan Westphal "Reality" (p. 10), 1994.
Heraclitus of Ephesus (2017). “Heraclitus on the two antithetical forces in life: Interdependent and mutually convertible aspects of One Cause”, p.8, Philaletheians UK