What is the basis for saying that the Gospel of Thomas was accepted as scripture by early Christians? In an answer here, Dick Harfield writes:


  we know that [the Gospel of Thomas] and (probably) Q were treated as scripture by early Christians.


Reading the Wikipedia article on the Gospel of Thomas, I see that there is scholarly disagreement over the dating of the Gospel of Thomas – some say before AD 100, while others say after.  But by the mid- to late-2nd century, the four gospels we recognize today were affirmed by Irenaeus and others, to the exclusion of the Gospel of Thomas.  Actual evidence from the first century seems sparse, and so my question:

Among those arguing for an early date for the Gospel of Thomas, what is the evidence that points to early Christians (i.e., 1st century or early 2nd century) considering it to be "scripture"?
There is a "Gospel of Thomas" and there is an "Infancy Gospel of Thomas" - they are two different documents.  

The former Gospel of Thomas - along with all other non-canonical Gospels - was roundly condemned by Cyril of Jerusalem in his fifth catechetical lecture:


  Then of the New Testament there are the four Gospels only, for the
  rest have false titles and are mischievous.  The Manichæans also wrote
  a Gospel according to Thomas, which being tinctured with the fragrance
  of the evangelic title corrupts the souls of the simple sort.


Aside from a possible quote from the book in Clement's 2nd Epistle (whose authenticity Eusebius seems to dispute), there is no evidence that any Church Father considered the Gospel of Thomas or any other apocryphal gospel to be canonical.  It is not included in the list given by Athanasius (Festal Letter XXXIX), nor in any of the lists enumerated by any local or ecumenical council, nor in the later Exact Exposition of the Orthodox Faith, by John of Damascus.

That is not to say that there were not some who called themselves "Christians" who would have considered the book to be Scripture, as historians suggest, but the sects who held these beliefs were considered to be/have been heretical by the Church of the Ecumenical Councils.