“Opening our modern edition of the New Testament, we find that Hebrews occupies the leaves between Philemon and James, that is between the thirteenth Pauline and the first Catholic Epistle. Does this collocation separate it from the Corpus Paulinum? Manuscript evidence shows that it does not. In the oldest uncials (S A B C) it follows second Thessalonians and precedes the Pastorals. This is also the position which it occupies in most MSS of the Bohairic Version and in the commentary of St. Ephraem… In the archetype or predecessors of Codex B, it stood between Galatians and Ephesians, as the series of sectional numbers on the margin of that Codex shows. In the Sahidic Version, it even preceded Galatians. The Syriac Versions, the later Greek MSS and the Latin MSS assign Hebrews the order to which we are accustomed, namely, fourteenth place at the end of the Paulines. That it earlier found a place tenth after the nine Letters to the Seven Churches, or after the four great Epistles, or within these in the fourth place is a strong testimony of its ascription to St. Paul. Still more eloquent is the order of the Chester-Beatty papyrus Codex of the early third century. Here Hebrews comes immediately after Romans.”
-William Leonard, Authorship of the Epistle to the Hebrews.