Per Rowan Williams’ Arius: Heresy and Tradition (rev. ed. 2001), here is what was adopted by a synod of bishops at Antioch, although a far smaller number than would later convene at Nicea:
We believe in one God, the Father, the ruler of all,
incomprehensible, immutable and unchanging, the providential
overseer and governor of all things, righteous and good, maker of
heaven and earth and all that is in them, Lord of the Law and the
prophets and the New Covenant; and in one Lord Jesus Christ, the
only-begotten Son, begotten not out of non-existence, but out of the
Father, not as a thing made but as a begotten being in the strict
sense, generated in an unutterable and indescribable fashion, since
only the Father who begat and the Son who was begotten know its
mode—“No one knows the Father except the Son, or the Son except
the Father.” He always exists and did not earlier on not exist. For
we have learned from the holy scriptures that he is the sole image
[of the Father], and is not unbegotten, since it is clear that he is, so
to speak, ‘from’ the Father. The scriptures call him a begotten son,
in the strict and proper sense—not just by convention, for it would
be irreverent and blasphemous to say this. Just so do we believe
that he is immutable and unchanging, not begotten or brought into
being by will or [only] conventionally speaking, in such a way that
he would seem to be generated out of non-existence, but begotten in
the way appropriate for him, not in the likeness or the nature of
anything that has come to be through him, or mixed with them at
all—which it is not lawful to imagine. Rather do we confess, then,
because he transcends all conception or understanding or thought,
that he was begotten out of the unbegotten Father, God the Word,
the true light, righteousness, Jesus Christ, the Lord and Savior of
all. For he is the image not of the will or anything else, but of the
actual hypostasis of the Father. This Son, God the Word, having
also been born and made flesh out of Mary the Mother of God, and
suffered, and died, rose from the dead and, when he had been taken
into heaven, took his seat at the right hand of the power of the Most
High, and is coming to judge living and dead.