The Ecclesiastical History of Socrates Scholasticus

After Peter, bishop of Alexandria, had suffered martyrdom under Diocletian, Achillas was installed in the episcopal office, whom Alexander succeeded, during the period of peace above referred to. He, in the fearless exercise of his functions for the instruction and government of the Church, attempted one day in the presence of the presbytery and the rest of his clergy, to explain, with perhaps too philosophical minuteness, that great theological mystery—the Unity of the Holy Trinity. A certain one of the presbyters under his jurisdiction, whose name was Arius, possessed of no inconsiderable logical acumen, imagining that the bishop was subtly teaching the same view of this subject as Sabellius the Libyan, from love of controversy took the opposite opinion to that of the Libyan, and as he thought vigorously responded to what was said by the bishop. ‘If,’ said he, ‘the Father begat the Son, he that was begotten had a beginning of existence: and from this it is evident, that there was a time when the Son was not. It therefore necessarily follows, that he had his substance from nothing.’