The Scripture says we are saved by grace through faith, and not of works. The Apostolic Fathers were unaminous in affirming the same whenever the issue came up:

And we, too, being called by His will in Christ Jesus, are not justified by ourselves, nor by our own wisdom, or understanding, or godliness, or works which we have wrought in holiness of heart; but by that faith through which, from the beginning, Almighty God has justified allmen; to whom be glory for ever and ever (1 Clem 32).

In whom, though now you see Him not, you believe, and believing, rejoice with joy unspeakable and full of glory; into which joy many desire to enter, knowing that by grace you are saved, not of works,  but by the will of God through Jesus Christ (Polycarp 1).

For were He to reward us according to our works, we should cease to be (Epistle to Magnesians, Chap 10).

This was not that He at all delighted in our sins, but that He simply endured them; nor that He approved the time of working iniquity which then was, but that He sought to form a mind conscious of righteousness, so that being convinced in that time of our unworthiness of attaining life through our own works, it should now, through the kindness of God, be vouchsafed to us; and having made it manifest that in ourselves we were unable to enter into the kingdom of God, we might through the power of God be made able (Epistle of Mathetes to Diognetus, Chap 9).

If you also desire [to possess] this faith, you likewise shall receive first of all the knowledge of the Father…And when you have attained this knowledge, with what joy do you think you will be filled? Or, how will you love Him who has first so loved you? And if you love Him, you will be an imitator of His kindness (Ibid., Chap 10).

The reason I end with the quotation from Mathetes is that it shows that works are not the means that one is saved, but they are something that a believer is compelled to do out of true conviction. Hence, works are the fruit of faith and the evidence (not cause) of salvation. This is why James writes, “I will show you my faith by what I do” (James 2:18).

It is to be expected that the Gospel of faith alone had remained intact among the first couple generations of believers. However, by the mid second century some chinks in the Christian armor seemingly begin to form. For example, Justin Martyr writes:

But though a man be a Scythian or a Persian, if he has the knowledge of God and of His Christ, and keeps the everlasting righteous decrees, he is circumcised with the good and useful circumcision, and is a friend of God, and God rejoices in his gifts and offerings (Dialogue with Trypho, Chapter 28).

Since those who did that which is universally, naturally, and eternally good are pleasing to God, they shall be saved through this Christ in the resurrection equally with those righteous men who were before them…those who believe in Him and live acceptably (Dialogue with Trypho, Chapter 45).

It seems pretty clear, taking Justin’s words alone and not inferring any presuppositions onto them, that he believed in faith+works.

Listening to Irenaeus today, it sounded to me that he taught something similar to Justin. The relevant chapter is AH 4.16. In this chapter, Irenaeus is arguing that the “moral law” as we call it today (or “law of nature” as the Fathers would have put it) is still in force, but the rules of the Mosaic Covenant are not. Irenaeus argued this in order to defang the Gnostics, who were often antinomian and hedonistic.  It starts in Paragraph 1:

Moreover, we learn from the Scripture itself, that God gave circumcision, not as the completer of righteousness, but as a sign, that the race of Abraham might continue recognisable.

Irenaeus starts with the above, teaching that circumcision never justified believers because its purpose never was to justify but rather to act as a sign. In the same chapter, he says the same of the Sabbath:

This same does Ezekiel the prophet say with regard to the Sabbaths: Also I gave them My Sabbaths, to be a sign between Me and them, that they might know that I am the Lord, that sanctify them.

Irenaeus speculates afterwards that circumcision was pointing to our need for having our hearts circumcised, and the Sabbath pointed to our need to “continue day by day in God’s service.” He then continues:

And that man was not justified by these things, but that they were given as a sign to the people, this fact shows—that Abraham himself, without circumcision and without observance of Sabbaths, believed God, and it was imputed unto him for righteousness; and he was called the friend of God (Par 2).

Ireneaus then speculates that the Law was not given to the patriarchs because they lived righteously without the need of the Law reminding them to live better lives:

Why, then, did the Lord not form the covenant for the fathers? Because the law was not established for righteous men. 1 Timothy 1:9 But the righteous fathers had the meaning of the Decalogue written in their hearts and souls, that is, they loved the God who made them, and did no injury to their neighbour. There was therefore no occasion that they should be cautioned by prohibitory mandates (Par 3).

Hence, the Law was made in order to warn unrighteous men (see 1 Tim 1:9). Righteous men do not need a Law to guide them, because they are at liberty to live righteously without rules micromanaging their behavior. However, the unrighteous Jews were not like this and therefore needed the Law to guide them (Par 4). The whole point of the Law was simply to show the Jews how to love God and their fellow man. These moral truisms are timeless according to Irenaeus:

Preparing man for this life, the Lord Himself did speak in His own person to all alike the words of the Decalogue; and therefore, in like manner, do they remain permanently with us, receiving by means of His advent in the flesh, extension and increase, but not abrogation (Par 4).

In Paragraph 5, Irenaeus sums up his argument by first saying that the Law put the Jews in “bondage,” sort of like a parent gives children rules for ethical behavior because children are immature and cannot decide for themselves. However, those who are free in Christ no longer have these rules, yet their moral obligations are indeed more exacting:

These things, therefore, which were given for bondage, and for a sign to them, He cancelled by the new covenant of liberty. But He has increased and widened those laws which are natural, and noble, and common to all, granting to men largely and without grudging, by means of adoption, to know God the Father, and to love Him with the whole heart, and to follow His word unswervingly, while they abstain not only from evil deeds, but even from the desire after them.

Irenaues then details how the sermon on the mount made clear that the Law (properly understood and applied) regulates not only behavior, but thoughts as well. Irenaeus then asserts:

[W]e shall give account to God not of deeds only, as slaves, but even of words and thoughts, as those who have truly received the power of liberty, in which [condition] a man is more severely tested, whether he will reverence, and fear, and love the Lord.

This would seem that our works are the means we are right before God, as the need to do good works does not pass away with the Law and they are used in God’s judgment of man. However, immediately afterwards Irenaeus affirms the orthodox Gospel:

And for this reason Peter says that we have not liberty as a cloak of maliciousness,1 Peter 2:16 but as the means of testing and evidencing faith.

Hence, Christian liberty gives us the opportunity to work righteousness not as slaves seeking remuneration for their works but rather to prove out our faith.