Luther: "It cannot be proved by the scriptures, that infant baptism was instituted by Christ, or begun by the first Christians after the apostles"

The Lutherans on the CARM board have been going at it with a few Baptists over infant baptism. Here's what caught my attention:

Martin Luther, the great father of the Reformation, says: "It cannot be proved by the scriptures, that infant baptism was instituted by Christ, or begun by the first Christians after the apostles. Apud Van. Inf. Bapt., part 2, p. 8.
Why are you Lutherans opposing your founder ?? [source]

The person citing this quote said he cited his source (Apud Van. Inf. Bapt., part 2, p. 8). This refers to a secondary source: "Vanity of Infant Baptism" by "R.A." or "A.R." from 1642, London. He then used this source for documentation (which cites the same thing). The quote certainly has been used frequently by Baptists. As I looked around for it, I didn't find any primary source citations. In regard to Vanity of Infant Baptism, one old author states:

This work was published in 1642. I have not been able to obtain it, but from the attention which was paid to it on both sides, we may naturally infer that it was then considered a work of a good deal of consequence. Dr. Featley has belabored this "tractate of A. R., entitled The ranitie of childrens baptitme," in fifteen pages of his Dippers' Dipt, that was published in 1645. He bestows upon the work and its author a large portion of those opprobrious epithets for which he was peculiarly distinguished. It is mentioned with much respect by Crosby, Ivimey, and other baptist historians; and in Teasdale's historical discourse, relative to the history of the first baptist church in New Haven, Conn., he informs us that Mrs. Eaton, the wife of the first Governor of that province, became tinctured with baptist sentiments from reading this book, which was loaned to her by lady Moody. This took place in 1664. The full name of the author I have never been able to learn.

[Edited to add: Tony Byrne of Theological Meditations submitted the following:

It appears that you are referencing "The second part of the vanity and childishnes of infants baptisme wherein the grounds from severall Scriptures usually brought for to justifie the same, are urged and answered. As also the nature of the divers covenants made with Abraham and his seed, briefly opened and applied." by Andrew Ritor [A.R.]. It seems that this work is available on EEBO (Early English Books Online) according to WorldCat. The first part of Ritor's work (which has nothing about Luther in it) can be obtained online here (click), but I don't think the second part is available online.]

And also:

"Concerning the time when Infants Baptisme was first invented, Luther in his Booke of Anabaptisme acknowledgeth, that it cannot be proved, by Sacred Scripture, that childrens Baptisme was instituted by Christ, or begun by the first Christians after the Apostles, for one thousand yeares since it came to be in use in the church, and was established by Pope Innocentius." A. R. [Andrew Ritor], The Second Part of the Vanity and Childishness of Infants Baptisme (London, 1642), 8.

Tony Byrne's help established that the quote in question isn't actually a direct quote. It's a summary statement based on Luther's treatise, Concerning Rebaptism (1528). I suggest if you really want to know what Luther felt about this subject, read the entire treatise. This is only a snippet of an extended argument (Luther makes multiple points).

In the second place, this is an important consideration: No heresy endures to the end, but always, as St. Peter says, soon comes to light and is revealed as disgraceful. So St. Paul mentions Jannes and Jambres and their like [II Tim. 3:8f.], whose folly is finally plain to all. Were child baptism now wrong God would certainly not have permitted it to continue so long, nor let it become so universally and thoroughly established in all Christendom, but it would sometime have gone down in disgrace. The fact that the Anabaptists now dishonor it does not mean anything final or injurious to it. Just as God has established that Christians in all the world have accepted the Bible as Bible, the Lord’s Prayer as Lord’s Prayer, and faith of a child as faith, so also he has established child baptism and kept it from being rejected while all kinds of heresies have disappeared which are much more recent and later than child baptism. This miracle of God is an indication that child baptism must be right. He has not so upheld the papacy, which also is an innovation and has never been accepted by all Christians of the world as has child baptism, the Bible, faith, or the Lord’s Prayer, etc.

You say, this does not prove that child baptism is certain. For there is no passage in Scripture for it. My answer: that is true. From Scripture we cannot clearly conclude that you could establish child baptism as a practice among the first Christians after the apostles. But you can well conclude that in our day no one may reject or neglect the practice of child baptism which has so long a tradition, since God actually not only has permitted it, but from the beginning so ordered, that it has not yet disappeared.

For where we see the work of God we should yield and believe in the same way as when we hear his Word, unless the plain Scripture tells us otherwise. I indeed am ready to let the papacy be considered as a work of God. But since Scripture is against it, I consider it as a work of God but not as a work of grace. It is a work of wrath from which to flee, as other plagues also are works of God, but works of wrath and displeasure. (LW 40:255-256)

Addendum
A Lutheran on the CARM boards maintains that the Luther's Concerning Rebaptism is not the source of the obscure quote in question.

I lean towards the translation of the obscure quote to be either a different translation or a less accurate translation. I believe it is an "actual quote" that may have morphed over the years originating from Luther's Concerning Rebaptism.

I've been through a number of situations like this. The secondary work referred to: "Apud Van. Inf. Bapt" dates from 1642. This tells me that if someone in 1642 had access to Luther's writings, they probably only had access to Luther's most popular writings. Brecht notes that Concerning Rebaptism is Luther's only major work against Anabaptist theology (there is a sermon from Luther on this topic that was often available as well throughout the centuries). As I've discovered in just about every instance of secondary Luther citations from the 16th-17th centuries, the primary source was not some unknown letter or lesser-known writing. Interestingly (at least to me) is that one of Luther's earliest papal critics (Cochlaeus) cites the same sort of sentiment against Luther (using Concerning Rebaptism), that Luther held that infant baptism cannot be proved from Scripture. In other words, this charge against Luther came on the scene early and gained popularity early, and did so because of Luther's writing, Concerning Rebaptism.

Often, if one finds a Luther citation that dates back to a secondary source from either the 16th or 17th Centuries, there can a wide dynamic range in the translation. Without having access to "Apud Van. Inf. Bapt," it's hard to know exactly which source the author used. Did he rely on another secondary source (like Cochlaeus), did he have a German copy of the treatise, or did he have a translation of the German in another language? When the quote was revised by from the old English to new English, did it morph is some way? This probably accounts for the slight variations between the LW translation and that allegedly taken from Apud Van. Inf. Bapt.

Probably the most humorous example of the misuse of a Luther quote I've been involved with was when I nailed Roman apologist Steve Ray for mis-citing Luther. Ray brought in two of his buddies, one a self-professed Pro-Romanist apologist, the other a lawyer, all spending weeks and weeks trying to prove I had the wrong source, and that the quote Steve Ray was using is from an unknown source that's out there somewhere. The quote Ray was using similarly dated back to secondary sources from the 16th and 17th Centuries. Some of Ray's buddies reluctantly agreed I had it right all along, Ray though still holds out the possibility that some mysterious Luther writing putting his particular spin on the quote he used may be out there.