Justin Martyr (100-165) is a key witness of the doctrine of creation from pre-existing material and the novelty that is creation ex nihilo. In his First Apology (an online version is available here), we find the following comments (emphasis added):
But we have received by tradition that God does not need the material offerings which men can give, seeing, indeed, that He Himself is the provider of all things. And we have been taught, and are convinced, and do believe, that He accepts those only who imitate the excellences which reside in Him, temperance, and justice, and philanthropy, and as many virtues as are peculiar to a God who is called by no proper name. And we have been taught that He in the beginning did of His goodness, for man's sake, create all things out of unformed matter; and if men by their works show themselves worthy of this His design, they are deemed worthy, and so we have received--of reigning in company with Him, being delivered from corruption and suffering. For as in the beginning He created us when we were not, so do we consider that, in like manner, those who choose what is pleasing to Him are, on account of their choice, deemed worthy of incorruption and of fellowship with Him. For the coming into being at first was not in our own power; and in order that we may follow those things which please Him, choosing them by means of the rational faculties He has Himself endowed us with, He both persuades us and leads us to faith. And we think it for the advantage of all men that they are not restrained from learning these. (First Apology, 10)
And that you may learn that it was from our teachers--we mean the account given through the prophets-- that Plato borrowed his statement that God, having altered matter which was shapeless, made the world, hear the very words spoken through Moses, who, as above shown, was the first prophet, and of greater antiquity than the Greek writers; and through whom the Spirit of prophecy, signifying how and from what materials God at first formed the world, spake thus: "In the beginning God created the heaven and the earth. And the earth was invisible and unfurnished, and darkness was upon the face of the deep; and the Spirit of God moved over the waters. And God said, Let there be light; and it was so." So that both Plato and they who agree with him, and we ourselves, have learned, and you also can be convinced, that by the word of God the whole world was made out of the substance spoken of before by Moses. And that which the poets call Erebus, we know was spoken of formerly by Moses. (First Apology, 59)
It is rather obvious from these passages that Justin believed everything was created, not ex nihilo, but out of a material substrate, and such is the teaching of the creation account in Genesis 1.