In this very short post, I will cite a few early church fathers and writers who all affirm the uncreated, eternal nature of the Son.
Chapter 6. Preserve harmony
Since therefore I have, in the persons before mentioned, beheld the whole multitude of you in faith and love, I exhort you to study to do all things with a divine harmony, while your bishop presides in the place of God, and your presbyters in the place of the assembly of the apostles, along with your deacons, who are most dear to me, and are entrusted with the ministry of Jesus Christ, who was with the Father BEFORE THE BEGINNING OF TIME, and in the end was revealed. Do all then, imitating the same divine conduct, pay respect to one another, and let no one look upon his neighbour after the flesh, but continually love each other in Jesus Christ. Let nothing exist among you that may divide you; but be united with your bishop, and those that preside over you, as a type and evidence of your immortality.(Ignatius of Antioch, Epistle to the Magnesians, AD 107-112; bold and capital emphasis mine)
Chapter 7. Beware of false teachers
For some are in the habit of carrying about the name [of Jesus Christ] in wicked guile, while yet they practise things unworthy of God, whom you must flee as you would wild beasts. For they are ravening dogs, who bite secretly, against whom you must be on your guard, inasmuch as they are men who can scarcely be cured. There is one Physician who is possessed both of flesh and spirit; both made AND NOT MADE; God existing in flesh; true life in death; both of Mary and of God; first passible and then impassible — even Jesus Christ our Lord. (Ignatius, Epistle to the Ephesians; bold and capital emphasis mine)
Chapter 3. Exhortations
Let not those who seem worthy of credit, but teach strange doctrines, 1 Timothy 1:3, 1 Timothy 6:3 fill you with apprehension. Stand firm, as does an anvil which is beaten. It is the part of a noble athlete to be wounded, and yet to conquer. And especially, we ought to bear all things for the sake of God, that He also may bear with us. Be ever becoming more zealous than what you are. Weigh carefully the times. Look for Him who is ABOVE ALL TIME, ETERNAL and invisible, yet who became visible for our sakes; impalpable and impassible, yet who became passible on our account; and who in every kind of way suffered for our sakes. (Ignatius, Epistle to Polycarp; bold and capital emphasis mine)
This next quotation refers to the Holy Spirit being uncreated and eternal as well:
There is one God, the Father of the living Word, who is His subsistent Wisdom and Power and Eternal Image: perfect Begetter of the perfect Begotten, Father of the only-begotten Son. There is one Lord, Only of the Only, God of God, Image and Likeness of Deity, Efficient Word, Wisdom comprehensive of the constitution of all things, and Power formative of the whole creation, true Son of true Father, Invisible of Invisible, and Incorruptible of Incorruptible, and Immortal of Immortal and Eternal of Eternal. And there is One Holy Spirit, having His subsistence from God, and being made manifest by the Son, to wit to men: Image of the Son, Perfect Image of the Perfect; Life, the Cause of the living; Holy Fount; Sanctity, the Supplier, or Leader, of Sanctification; in whom is manifested God the Father, who is above all and in all, and God the Son, who is through all. There is a perfect Trinity, in glory and eternity and sovereignty, neither divided nor estranged. Wherefore there is nothing either created or in servitude in the Trinity; nor anything superinduced, as if at some former period it was non-existent, and at some later period it was introduced. And thus neither was the Son ever wanting to the Father, nor the Spirit to the Son; but without variation and without change, the same Trinity abides ever. (St. Gregory Thaumaturgus (“The Wonderworker”), A Declaration of Faith, AD 265; bold emphasis mine)
Chapter 29. Of the Christian Religion, and of the Union of Jesus with the Father.
Some one may perhaps ask how, when we say that we worship one God only, we nevertheless assert that there are two, God the Father and God the Son: which assertion has driven many into the greatest error. For when the things which we say seem to them probable, they consider that we fail in this one point alone, that we confess that there is another God, and that He is mortal. We have already spoken of His mortality: now let us teach concerning His unity. When we speak of God the Father and God the Son, we do not speak of them as different, nor do we separate each: because the Father cannot exist without the Son, nor can the Son be separated from the Father, since the name of Father cannot be given without the Son, nor can the Son be begotten without the Father. Since, therefore, the Father makes the Son, and the Son the Father, they both have one mind, one spirit, one substance; but the former is as it were an overflowing fountain, the latter as a stream flowing forth from it: the former as the sun, the latter as it were a ray extended from the sun. And since He is both faithful to the Most High Father, and beloved by Him, He is not separated from Him; just as the stream is not separated from the fountain, nor the ray from the sun: for the water of the fountain is in the stream, and the light of the sun is in the ray: just as the voice cannot be separated from the mouth, nor the strength or hand from the body. When, therefore, He is also spoken of by the prophets as the hand, and strength, and word of God, there is plainly no separation; for the tongue, which is the minister of speech, and the hand, in which the strength is situated, are inseparable portions of the body.
We may use an example more closely connected with us. When any one has a son whom he especially loves, who is still in the house, and in the power of his father, although he concede to him the name and power of a master, yet by the civil law the house is one, and one person is called master. So this world is the one house of God; and the Son and the Father, who unanimously inhabit the world, are one God, for the one is as two, and the two are as one. Nor is that wonderful, since the Son is in the Father, for the Father loves the Son, and the Father is in the Son; for He faithfully obeys the will of the Father, nor does He ever do nor has done anything except what the Father either willed or commanded. Lastly, that the Father and the Son are but one God, Isaiah showed in that passage which we have brought forward before, when he said: Isaiah 45:14 They shall fall down unto You, and make supplication unto You, since God is in You, and there is no other God besides You. And he also speaks to the same purport in another place: Isaiah 44:6 Thus says God the King of Israel, and His Redeemer, the everlasting God; I am the first, and I am the last; and beside me there is no God. When he had set forth two persons, one of God the King, that is, Christ, and the other of God the Father, who after His passion raised Him from the dead, as we have said that the prophet Hosea showed, Hosea 13:14 who said, I will redeem Him from the power of the grave: nevertheless, with reference to each person, he introduced the words, and beside me there is no God, when he might have said beside us; but it was not right that a separation of so close a relationship should be made by the use of the plural number. For there is one God alone, free, most high, without any origin; for He Himself is the origin of all things, and in Him at once both the Son and all things are contained. Wherefore, since the mind and will of the one is in the other, or rather, since there is one in both, both are justly called one God; for whatever is in the Father flows on to the Son, and whatever is in the Son descends from the Father. Therefore that highest and matchless God cannot be worshipped except through the Son. He who thinks that he worships the Father only, as he does not worship the Son, so he does not worship even the Father. But he who receives the Son, and bears His name, he truly together with the Son worships the Father also, since the Son is the ambassador, and messenger, and priest of the Most High Father. He is the door of the greatest temple, He the way of light, He the guide to salvation, He the gate of life. (Lactantius, Divine Institutes, Book IV Of true wisdom and religion, AD 307; bold emphasis mine)
7. Believe also in the Son of God, One and Only, our Lord Jesus Christ, Who was begotten God of God, begotten Life of Life, begotten Light of Light , Who is in all things like to Him that begot, Who received not His being in time, but was before all ages eternally and incomprehensibly begotten of the Father: The Wisdom and the Power of God, and His Righteousness personally subsisting: Who sits on the right hand of the Father before all ages.
For the throne at God’s right hand He received not, as some have thought, because of His patient endurance, being crowned as it were by God after His Passion; but throughout His being — a being by eternal generation — He holds His royal dignity, and shares the Father’s seat, being God and Wisdom and Power, as has been said; reigning together with the Father, and creating all things for the Father, yet lacking nothing in the dignity of Godhead, and knowing Him that has begotten Him, even as He is known of Him that has begotten; and to speak briefly, remember thou what is written in the Gospels, that none knows the Son but the Father, neither knows any the Father save the Son.
8. Further, do thou neither separate the Son from the Father, nor by making a confusion believe in a Son-Fatherhood ; but believe that of One God there is One Only-begotten Son, who is before all ages God the Word; not the uttered word diffused into the air, nor to be likened to impersonal words ; but the Word the Son, Maker of all who partake of reason, the Word who hears the Father, and Himself speaks. And on these points, should God permit, we will speak more at large in due season; for we do not forget our present purpose to give a summary introduction to the Faith. (Cyril of Jerusalem, Catechetical Lectures, Lecture 4, AD 350; bold emphasis mine)