Authors: Eudemos of Rhodes (fourth century BCE) as cited by Damascius, Difficulties and Solutions of First Principles 125 (link to Greek text and full work).
Comments: Eudemos of Rhodes was a student of Aristotle and Damascius, who cites Eudemos here, was a neo-Platonist in the sixth century CE. The passage presents in a positive way the cosmic dualism of the Magians and the Iranian people.
Source of the translation: Translated by Harland.
[Aspects of Magians’ worldview]
Regarding the Magians and the entire Iranian (areion) people, just as Eudemos also writes, some call everything that is intelligible and uniﬁed “Place” (topos) and others call it “Time” (chronos). From this either a good god and an evil daimon have separated. or light and darkness have separated before these, as some say. However, they also posit, after the undifferentiated nature, the existence of a double series of higher beings of which Oromasdes [Ahura Mazda] controls one and Arimanios [Angra Mainyu] the other.