The Ecclesiastical History of Sozomen

After there had been many synods held in Egypt, and the contest had still continued to increase in violence, the report of the dissension reached the palace, and Constantine was thereby greatly troubled; for just at this period, when religion was beginning to be more generally propagated, many were deterred by the difference in doctrines from embracing Christianity. The emperor openly charged Arius and Alexander with having originated this disturbance, and wrote to rebuke them for having made a controversy public which it was in their power to have concealed, and for having contentiously agitated a question which ought never to have been mooted, or upon which, at least, their opinion ought to have been given quietly. He told them that they ought not to have separated from others on account of difference of sentiment concerning certain points of doctrine.

For concerning the Divine Providence men ought necessarily to hold one and the same belief; but the minute researches in this province, especially if they do not bring them to the one opinion, must be retained in secret according to all reason. He exhorted them to put away all loose talk about such points, and to be of one mind; for he had been not a little grieved, and on this account he had renounced his intention of visiting the cities of the East. It was in this strain that he wrote to Alexander and to Arius, reproving and exhorting them both.

Constantine was also deeply grieved at the diversity of opinion which prevailed concerning the celebration of the Passover; for some of the cities in the East differed on this point, although they did not withhold from communion with one another; they kept the festival more according to the manner of the Jews, and as was natural by this divergence, detracted from the splendor of the festal sacrifice. The emperor zealously endeavored to remove both these causes of dissension from the church; and thinking to be able to remove the evil before it advanced to greater proportions, he sent one who was honored for his faith, his virtuous life, and most approved in those former times for his confessions about this doctrine, to reconcile those who were divided on account of doctrine in Egypt, and those who in the East differed about the Passover. This man was Hosius, bishop of Cordova.