From “The Epistle of Barnabas” (70-130AD)
The author of the Epistle of Barnabas is unknown, but many consider him to simply be who he said he was, Barnabas, the associate of Paul who is mentioned in the Book of Acts. The letter was written to new converts to Christianity:
The way of darkness is crooked, and it is full of cursing. It is the way of eternal death with punishment. (“Epistle of Barnabas”)
From “Second Clement” (150AD)
This epistle was written by an Early Church Father as a recorded sermon (ascribed to Clement of Rome). Clement was bishop of Rome from 88 to 98AD, and his teaching reflects the early traditions of the Church:
If we do the will of Christ, we shall obtain rest; but if not, if we neglect his commandments, nothing will rescue us from eternal punishment (“Second Clement” 5:5)
From Justin Martyr (151AD)
An early believer and apologist for the Christian faith, Justin Martyr was born in Palestine and was martyred in Rome under Marcus Aurelius. He wrote several important defenses of Christianity, addressed to leaders of the Roman Empire:
No more is it possible for the evildoer, the avaricious, and the treacherous to hide from God than it is for the virtuous. Every man will receive the eternal punishment or reward which his actions deserve. Indeed, if all men recognized this, no one would choose evil even for a short time, knowing that he would incur the eternal sentence of fire. On the contrary, he would take every means to control himself and to adorn himself in virtue, so that he might obtain the good gifts of God and escape the punishments (“First Apology” 12).
We have been taught that only they may aim at immortality who have lived a holy and virtuous life near to God. We believe that they who live wickedly and do not repent will be punished in everlasting fire (“First Apology” 21).
[Jesus] shall come from the heavens in glory with his angelic host, when he shall raise the bodies of all the men who ever lived. Then he will clothe the worthy in immortality; but the wicked, clothed in eternal sensibility, he will commit to the eternal fire, along with the evil demons (“First Apology” 52).
From “The Martyrdom of Polycarp” (155AD)
This work was written by an Early Church Father (unknown author) and is dated very early in the history of Christianity. It describes the death of Polycarp, a disciple of the Apostle John, and also describes early teachings of the church:
Fixing their minds on the grace of Christ, [the martyrs] despised worldly tortures and purchased eternal life with but a single hour. To them, the fire of their cruel torturers was cold. They kept before their eyes their escape from the eternal and unquenchable fire (“Martyrdom of Polycarp” 2:3)
From Tatian (160AD)
Tatian was an early Assyrian believer who moved to Rome as a pagan and eventually became a Christian. Interestingly, he read the Jewish Scriptures and from these became convinced that other pagan ideas about the world were simply false. He was a student of Justin Martyr and wrote about the unreasonableness of paganism and the truth of Christianity:
We who are now easily susceptible to death, will afterwards receive immortality with either enjoyment or with pain.
From Athenagoras of Athens (175AD)
Athenagoras was a philosopher and citizen of Athens who became a Christian (possibly from Platonism) and wrote two important apologetic works; “Apology” or “Embassy for the Christians”, and a “Treatise on the Resurrection”:
We are persuaded that when we are removed from the present life we will live another life, better than the present one...or, if they fall with the rest, they will endure a worse life, one in fire. For God has not made us as sheep or beasts of burden, who are mere by-products. For animals perish and are annihilated. On these grounds, it is not likely that we would wish to do evil. (“Apology”)
From Theophilus of Antioch (181AD)
Theophilus was the Patriarch of Antioch from 169 to 183AD. He was born a pagan and converted to Christianity after reading the scriptures. He was very zealous about protecting the orthodoxy of the earliest believers and he wrote a defense of the faith to a man named Autolycus:
Give studious attention to the prophetic writings [the Bible] and they will lead you on a clearer path to escape the eternal punishments and to obtain the eternal good things of God. . . . [God] will examine everything and will judge justly, granting recompense to each according to merit. To those who seek immortality by the patient exercise of good works, he will give everlasting life, joy, peace, rest, and all good things. . . . For the unbelievers and for the contemptuous, and for those who do not submit to the truth but assent to iniquity, when they have been involved in adulteries, and fornications, and homosexualities, and avarice, and in lawless idolatries, there will be wrath and indignation, tribulation and anguish; and in the end, such men as these will be detained in everlasting fire (“To Autolycus” 1:14)
From Irenaeus (189AD)
Irenaeus was bishop of Lugdunum in Gaul (now Lyon, France) at the end of the second century. He was a discplie of Polycarp and a notable early apologist for the faith. He wrote several volumes defending the faith against Gnosticism and other early heresies of the Church:
[God will] send the spiritual forces of wickedness, and the angels who transgressed and became apostates, and the impious, unjust, lawless, and blasphemous among men into everlasting fire (“Against Heresies” 1:10:1)
The penalty increases for those who do not believe the Word of God and despise his coming. . . . [I]t is not merely temporal, but eternal. To whomsoever the Lord shall say, ‘Depart from me, accursed ones, into the everlasting fire,’ they will be damned forever (“Against Heresies” 4:28:2)
From Clement of Alexandria (195AD)
Titus Flavius Clemens was the first significant and recorded Christian from the church of Alexandria, Egypt. His parents were Greek and he was raised with a solid, formal Greek education. While he had a tendency to blend Greek and Christian philosophies, his view on the issue of Hell was derived from the scriptures:
All souls are immortal, even those of the wicked. Yet, it would be better for them if they were not deathless. For they are punished with the endless vengeance of quenchless fire. Since they do not die, it is impossible for them to have an end put to their misery. (from a post-Nicene manuscript fragment)
From Tertullian (197AD)
Quintus Septimius Florens Tertullianus was a Romanized African citizen who was born in Carthage (now Tunisia). He became a Christian and was a powerful and influential apologist for the faith, writing prolifically in defense of the doctrines of orthodoxy:
After the present age is ended he will judge his worshipers for a reward of eternal life and the godless for a fire equally perpetual and unending (“Apology” 18:3)
Then will the entire race of men be restored to receive its just deserts according to what it has merited in this period of good and evil, and thereafter to have these paid out in an immeasurable and unending eternity. Then there will be neither death again nor resurrection again, but we shall be always the same as we are now, without changing. The worshipers of God shall always be with God, clothed in the proper substance of eternity. But the godless and those who have not turned wholly to God will be punished in fire equally unending, and they shall have from the very nature of this fire, divine as it were, a supply of incorruptibility (“Apology” 44:12–13).
From Hippolytus of Rome (212AD)
Hippolytus was one of the most prolific writers of the early Church, and he was often at theological odds with the early Popes and church leaders of his time. He appears to have been a student of Irenaeus, and wrote MANY volumes of history, apologetics and Biblical teaching:
Standing before [Christ’s] judgment, all of them, men, angels, and demons, crying out in one voice, shall say: ‘Just is your judgment!’ And the righteousness of that cry will be apparent in the recompense made to each. To those who have done well, everlasting enjoyment shall be given; while to the lovers of evil shall be given eternal punishment. The unquenchable and unending fire awaits these latter, and a certain fiery worm which does not die and which does not waste the body but continually bursts forth from the body with unceasing pain. No sleep will give them rest; no night will soothe them; no death will deliver them from punishment; no appeal of interceding friends will profit them (“Against the Greeks 3”)
From Felix Minucius (226AD)
Felix Marcus Minucius is perhaps the earliest known Latin apologist for the Christian faith. He wrote “Octavius”, a dialogue on Christianity between a non-believer named Caecilius Natalis and a Christian named Octavius Januarius (who was a lawyer, friend and student of Minucius Felix:
I am not ignorant of the fact that many, in the consciousness of what they deserve, would rather hope than actually believe that there is nothing for them after death. They would prefer to be annihilated rather than be restored for punishment... Nor is there either measure nor end to these torments. That clever fire burns the limbs and restores them, wears them away and yet sustains them, just as fiery thunderbolts strike bodies but do not consume them (“Octavius” 34:12–5:3)
From Cyprian of Carthage (252 AD)
Thascius Caecilius Cyprianus was bishop at Carthage. He had an excellent Greek education and wrote several key letters and treatises in which he discussed doctrines of the Church:
An ever-burning Gehenna and the punishment of being devoured by living flames will consume the condemned; nor will there be any way in which the tormented can ever have respite or be at an end. Souls along with their bodies will be preserved for suffering in unlimited agonies. . . . The grief at punishment will then be without the fruit of repentance; weeping will be useless, and prayer ineffectual. Too late will they believe in eternal punishment, who would not believe in eternal life (“To Demetrian” 24)
From Lactantius (307AD)
Lucius Caelius Firmianus Lactantius was a Latin speaking native of North Africa. He was an expert in rhetoric and he taught the subject in the city of Nicomedia at the request of Emperor Diocletian. He also wrote several apologetic and doctrinal works:
[T]he sacred writings inform us in what manner the wicked are to undergo punishment. For because they have committed sins in their bodies, they will again be clothed with flesh, that they may make atonement in their bodies; and yet it will not be that flesh with which God clothed man, like this our earthly body, but indestructible, and abiding forever… (“Divine Institutes” 7:21)
From Cyril of Jerusalem (350AD)
Cyril was a well respected theologian of the early Church and a bishop of the church at Jerusalem. He wrote twenty three teaching lectures on the doctrines of the Church and delivered these lectures while he was a presbyter in Jerusalem:
We shall be raised therefore, all with our bodies eternal, but not all with bodies alike: for if a man is righteous, he will receive a heavenly body, that he may be able worthily to hold converse with angels; but if a man is a sinner, he shall receive an eternal body, fitted to endure the penalties of sins, that he may burn eternally in fire, nor ever be consumed… (“Catechetical Lectures” 18:19)
The Earliest Teaching 
Souls live on after the grave. Even those who are assigned to Hell are “immortal”, “indestructible” and “abide forever” Those assigned to Hell will be “detained in everlasting fire” for a period of time that is as “equally perpetual and unending” as the eternal life of those who are in Heaven. 
The rebellious will exist in Hell with an “eternal body, fitted to endure the penalties of sins”. They will “burn eternally in fire” and they will never “be consumed” Those tormented in Hell will never “have respite” and their torment will never “be at an end”. “Souls along with their bodies will be preserved for suffering in unlimited agonies” 
Souls in Hell will NOT be allowed to die or cease to exist. “They would prefer to be annihilated rather than be restored for punishment”, but this is simply not the case. The fire of Hell is “clever” and “burns the limbs and restores them, wears them away and yet sustains them, just as fiery thunderbolts strike bodies but do not consume them.” 
The torment suffered by those in Hell will be incredibly unbearable. It will feel as though “a certain fiery worm which does not die and which does not waste the body” will continually burst forth from the body “with unceasing pain”.