Sextus Empiricus Pyrrhoniae Hypotyposes 3.24.205

[205] And with us it is sinful to marry one’s mother or one’s own sister ; but the Persians, and especially those of them who are reputed to practise wisdom— namely, the Magi,—marry their mothers; and the Egyptians ¹ take their sisters in marriage, even as the poet says ² — Moreover, Zeno of Citium says that it is not amiss for a man to rub his mother’s private part with his own private part, just as no one would say it was bad for him to rub any other part of her body with his hand. Chrysippus, ³ too, in his book The State approves of a father getting children by his daughter, a mother by her son, and a brother by his sister. And Plato, ⁴ in more general terms, has declared that wives ought to be held in common.