Clement:
The Ante-Nicene Fathers, Volume I: The Apostolic Fathers with Justin Martyr and Irenaeus (A. Roberts, J. Donaldson & A. C. Coxe, Ed.) - Chap XVI
We have declared [our message] in His presence: He is, as it were, a child, and like a root in thirsty ground; He has no form nor glory, yea, we saw Him, and He had no form nor comeliness; but His form was without eminence, yea, deficient in comparison with the [ordinary] form of men. He is a man exposed to stripes and suffering, anti acquainted with the endurance of grief: for His countenance was turned away; He was despised, and not esteemed. He bears our iniquities, and is in sorrow for our sakes; yet we supposed that [on His own account] He was exposed to labour, and stripes, and affliction. But He was wounded for our transgressions, and bruised for our iniquities. The chastisement of our peace was upon Him, and by His stripes we were healed. All we, like sheep, have gone astray; [every] man has wandered in his own way; and the Lord has delivered Him up for our sins, while He in the midst of His sufferings opened not His mouth. He was brought as a sheep to the slaughter, and as a lamb before her shearer is dumb, so He opened not His mouth. In His humiliation His judgment was taken away; who shall declare His generation? for His life is taken from the earth. For the transgressions of my people was He brought down to death. And I will give the wicked for His sepulcher, and the rich for His death, because He did no iniquity, neither was guile found in His mouth. And the Lord is pleased to purify Him by stripes. If you make an offering for sin, your soul shall see a long-lived seed. And the Lord is pleased to relieve Him of the affliction of His soul, to show Him light, and to form Him with understanding, to justify the Just One who ministers well to many; and He Himself shall carry their sins. On this account He shall inherit many, and shall divide the spoil of the strong; because His soul was delivered to death, and He was reckoned among the transgressors, and He bore the sins of many, and for their sins was He delivered.”
Justin:
XCV — Christ took upon Himself the curse due to us.
For the whole human race will be found to be under a curse. For it is written in the law of Moses, ‘Cursed is every one that continueth not in all things that are written in the book of the law to do them’ [Deut 27:26]. And no one has accurately done all, nor will you venture to deny this; but some more and some less than others have observed the ordinances enjoined. But if those who are under this law appear to be under a curse for not having observed all the requirements, how much more shall all the nations appear to be under a curse who practise idolatry, who seduce youths, and commit other crimes? If, then, the Father of all wished His Christ for the whole human family to take upon Him the curses of all, knowing that, after He had been crucified and was dead, He would raise Him up, why do you argue about Him, who submitted to suffer these things according to the Father’s will, as if He were accursed, and do not rather bewail yourselves? For although His Father caused Him to suffer these things in behalf of the human family, yet you did not commit the deed as in obedience to the will of God. For you did not practise piety when you slew the prophets. And let none of you say: If His Father wished Him to suffer this, in order that by His stripes the human race might be healed, we have done no wrong. If, indeed, you repent of your sins, and recognise Him to be Christ, and observe His commandments, then you may assert this; for, as I have said before, remission of sins shall be yours. But if you curse Him and them that believe on Him, and, when you have the power, put them to death, how is it possible that requisition shall not be made of you, as of unrighteous and sinful men, altogether hard-hearted and without understanding, because you laid your hands on Him?
In William Lane Craig’s soon to be released book defending Penal Substitution he goes into more depth and documentation of the early church fathers showing that Penal Substitution was a live option. Listen here as he quotes some fathers teaching Penal Substitution:
[youtube]http://www.youtube.com/watch?v=N2d2d7fnFnE[/youtube]