The Early Church Fathers on various topics: This was a 3700 hour project which included going through 22896 pages of the 38 volume set called Ante Nicene, Nicene, Post Nicene Fathers. I compiled 255 pages of quotes showing that the Early Church was always and completely Catholic. All of these quotes can be verified and found from the source which is free online.
Clement of Rome Recognitions book 7 ch 35 (27-97 ad)
So, then, if they were sure of this, that the punishment of eternal fire awaits those who do not worship God, when would they cease warning and exhorting?
Justin Martyr 155ad Second Apology Ch 9 (100-165 ad)
And that no one may say what is said by those who are deemed philosophers, that our assertions that the wicked are punished in eternal fire are big words and bugbears, and that we wish men to live virtuously through fear, and not because such a life is good and pleasant; I will briefly reply to this, that if this be not so, God does not exist; or, if He exists, He cares not for men and neither virtue nor vice is anything, and, as we said before, lawgivers unjustly punish those who transgress good commandments
Hyppolytus Against Plato, On the Cause of the Universe par 3 (170-236 ad)
since to those who have done well shall be assigned righteously eternal bliss, and to the lovers of iniquity shall be given eternal punishment. And the fire which is un-quenchable and without end awaits these latter, and a certain fiery worm which dieth not, and which does not waste the body, but continues bursting forth from the body with unending pain.
Archelaus Acts of the Disputation with the Heresia par 12
Therefore receive ye this third testimony, that I am an elect apostle of Christ; and if ye choose to accept my words, ye will find salvation; but if ye refuse them, eternal fire will have you to consume you.
Cyprian of Carthage epistle 60 par 2 (200-270 ad)
What more he may wish he must seek thence, from such gain as takes men away from the banquet of Abraham, and Isaac, and Jacob, and leads them down, sadly and perniciously fattened in this world, to the eternal torments of hunger and thirst
Lactantius Divine Institutes book 6 (290-350 ad)
We therefore speak better and more truly, who say that the two ways belong to heaven and hell, because immortality is promised to the righteous, and everlasting punishment is threatened to the unrighteous.
John Chrysostom Homily 9 on 1 Corinthians 3:12-15 (347-407 ad)
THIS is no small subject of enquiry which we propose, but rather about things which are of the first necessity and which all men enquire about; namely, whether hell fire have any end. For that it hath no end Christ indeed declared when he said, "Their fire shall not be quenched, and their worm shall not die.
John Chrysostom Homily 6 on John’s gospel (347-407 ad)
For though we have all faith and all knowledge of the Scriptures, yet if we be naked and destitute of the protection derived from (holy) living, there is nothing to hinder us from being hurried into the fire of hell, and burning for ever in the unquenchable flame. For as they who have done good shall rise to life everlasting, so they who have dared the contrary shall rise to everlasting punishment, which never has an end.
John Chrysostom Homily 17 on Statues par 15 (347-407 ad)
For the things present, whatever they are, are endurable, and have an end; but the torments there are immortal, and interminable!
John Chrysostom Homily 3 on Second Thessalonians (347-407 ad)
For the fear even from bare words is sufficient, though we do not fully unfold their meaning. But that it is not temporary, hear Paul now saying, concerning those who know not God, and who do not believe in the Gospel, that "they shall suffer punishment, even eternal destruction. How then is that temporary which is everlasting?
John Chrysostom Homily 9 on First Corinthians (347-407 ad)
As I said then; that it hath no end, Christ has declared. Paul also saith, in pointing out the eternity of the punishment, that the sinners "shall pay the penalty of destruction, and that for ever" neither fornicators. nor adulterers, nor effeminate, shall inherit the the kingdom of God."
John Cassian Conference 23 ch 15 (360-435 ad)
For whoever after baptism and the knowledge of God falls into that death, must know that he will either have to be cleansed, not by the daily grace of Christ, i.e., an easy forgiveness, which our Lord when at any moment He is prayed to, is wont to grant to our errors, but by a lifelong affliction of penitence and penal sorrow, or else will be hereafter consigned to the punishment of eternal fire for them, as the same Apostle thus declares: effeminate, nor defilers of themselves with mankind, nor thieves, nor covetous persons, nor drunkards, nor railers, nor extortioners shall possess the kingdom of God."
Augustine Exposition on Psalm 81 par 19 (354-430 ad)
If therefore all those works "shall not possess the kingdom of God" (yea not the works, but "they that do such things;" for such works there shall be none in the fire: for they shall not, while burning in that fire, be committing theft or adultery; but "they that do such things shall not possess the kingdom of God"); they shall not therefore be on the right hand
Augustine Concerning the Nature of Good Against the Manicheans ch 38 (354-430 ad)
For neither is eternal fire itself, which is to torture the impious, an evil nature, since it has its measure, its form and its order depraved by no iniquity; but it is an evil torture for the damned, to whose sins it is due. For neither is yonder light, because it tortures the blear-eyed, an evil nature.