hank you for the question on the early Church Fathers’ teaching on the “Trinity”, “What Church Fathers taught on the Trinity before Arius?”
I cite this website for one’s reading: Quotes from the Early Church Fathers: on the Trinity.
According to this website, they list the following Early Church Fathers:
A. Ignatius a.d. 30–107
“Since, also, there is but one unbegotten Being, God, even the Father; and one only-begotten Son, God, the Word and man; and one Comforter, the Spirit of truth; and also one preaching, and one faith, and one baptism;” The Epistle of Ignatius to the Philadelphians Chapter IV
B. Justin Martyr a.d. 110–165
“Since, also, there is but one unbegotten Being, God, even the Father; and one only-begotten Son, God, the Word and man; and one Comforter, the Spirit of truth; and also one preaching, and one faith, and one baptism;” The Epistle of Ignatius to the Philadelphians Chapter IV
C. Justin Martyr a.d. 110–165
“For, in the name of God, the Father and Lord of the universe, and of our Saviour Jesus Christ, and of the Holy Spirit, they then receive the washing with water.” The First Apology Chapter LXI
There are other Early Church Fathers and one can read the rest of them. The belief in the plurality of the Godhead was taught by the Early Church Fathers prior to the Council of Nicea in 325 CE.
The critical question is not what the Early Church Father believed or taught but on what bases did they come to that conclusion from the Scriptures. It was not a matter of their own opinion, but their understanding of the Scriptures.
For more perspectives:
https://www.quora.com/What-Church-Fathers-taught-on-the-Trinity-before-Arius