Quoted from Eusebius, Preparation for the Gospel
Book VI, Chap. X, p. 275c-d:
Among the Persians it was lawful to marry their daughters, and sisters, and mothers: and these unholy marriages the Persians practiced not only in that country and that clime, but also any of them who migrated from Persia, those who are called Magusaei continue to practice the same iniquity, handing down the same laws and customs to their children in succession.
Book VI, Chap. X, p. 279a:
...the Magusaei marry their daughters not only in Persia, but also in every nation where they may dwell, observing the laws of their forefathers, and the initiatory rites of their mysteries.