Quoted by Athanasius in
On the Synods 16.2-5.
This letter provides a statement of belief "from our forefathers" according to Arius. It's notable for distinguishing the theology of Arius from other theologies from Valentinus, Manicheans, Sabellius, and Hieracas. It's also notable for its use of Hebrews and again for referencing a large number of other church leaders alongside Arius, including Euzoios who later baptized Constantius, as seen from (xx).
I have bracketed the phrase "whom the Arians (later) set up (as bishop) at Alexandria" as falling after the true end of the quoted letter. This part of the letter is quoted in Epiphanius,
Panarion 2.69.
It is a later letter with a different audience (Alexander of Alexandria) than the letter to Eusebius of Nicomedia. This letter does not present the idea that the Son was created out of nothing, as in (xxvi), but it still says that the Son is "neither eternal nor co-eternal," with the more reserved language "begotten apart from time before all things."
(xxviii) Arius to Alexander of Alexandria [ca. 318-325]
https://www.fourthcentury.com/urkunde-6/
(1.) The priests and deacons to our blessed father and bishop, Alexander; greetings in the Lord.
(2.) Our faith from our forefathers, which also we learned from you, blessed father, is this: We acknowledge One God, alone unbegotten, alone everlasting, alone without beginning, alone true, alone having immortality, alone wise, alone good, alone sovereign, judge, governor, and provider of all, unalterable and unchangeable, just and good, God of the Law and the Prophets and the New Testament; who begat an only-begotten Son before time and the ages, through whom he made both the ages [Heb 1:2] and all that was made; who begot Him not in appearance, but in reality; and that he made him subsist at his own will, unalterable and unchangeable, the perfect creature (ktisma) of God, but not as one of the creatures; offspring, but not as one of the other things begotten; (3.) nor as Valentinus pronounced that the offspring of the Father was an emanation (probolē); nor as the Manicheans taught that the offspring was a one-in-essence-portion (meros homoousion) of the Father; nor as Sabellius, dividing the Monad, speaks of a Son-Father; nor as Hieracas speaks of one torch [lit] from another, or as a lamp divided into two; nor that he who existed before was later generated or created anew into a Son, as you yourself, O blessed father, have often condemned both in church services and in council meetings; but, as we say, he was created at the will of God, before time and before the ages, and came to life and being from the Father, and the glories which coexist in him are from the Father.
(4.) For when giving to him [the Son] the inheritance of all things [Heb 1:2], the Father did not deprive himself of what he has without beginning in himself; for he is the source of all things. Thus there are three subsisting realities (hypostaseis). And God, being the cause of all that happens, is absolutely alone without beginning; but the Son, begotten apart from time by the Father, and created (ktistheis) and founded before the ages, was not in existence before his generation, but was begotten apart from time before all things, and he alone came into existence (hypestē) from the Father. For he is neither eternal nor co-eternal nor co-unbegotten with the Father, nor does he have his being together with the Father, as some speak of relations, introducing two unbegotten beginnings. But God is before all things as monad and beginning of all. Therefore he is also before the Son, as we have learned also from your public preaching in the church.
(5.) Therefore he thus has his being from God; and glories, and life, and all things have been given over to him; in this way God is his beginning. For he is over him, as his God and being before him. But if the expressions from him [Rom. 11:36] and from the womb [Ps. 109:3 (LXX), 110:3 English] and I came from the Father, and I have come [John 16:28], are understood by some to mean that he is part of him [the Father], one in essence or as an emanation, then the Father is, according to them, compounded and divisible and alterable and material, and, as far as their belief goes, the incorporeal God endures a body.
(6.) I pray that you fare well in the Lord, blessed father. Arius; the priests Aethales, Achilles, Carpones, Sarmatas and Arius; the deacons Euzoios, Lucius, Julius, Menas, Helladius, and Gaius; the bishops Secundas of the Pentapolis, Theonas of Libya, and Pistus [whom the Arians (later) set up (as bishop) at Alexandria].