Ben David
https://books.google.com/books?id=GX4UAAAAYAAJ&pg=PA148
https://books.google.com/books?id=GX4UAAAAYAAJ&pg=PA320
https://books.google.com/books?id=GX4UAAAAYAAJ&pg=PA275
Thomas Burgess
https://archive.org/details/lettertoclergyof00burg/
https://archive.org/details/lettertoclergyof00burg/page/20/mode/2up
The peculiarities which distinguish 1 John v. 7, from other passages of Scripture, may, I think, be justly considered as tests of quotation, or of allusion to it, which will be the more probable in proportion to their antiquity. These peculiarities are the connumeration of the Word with the Father and the Holy Spirit,—the citation of the Three Divine Persons, as joint witnesses,—and the unity of the Three.
The passage of Theophilus may be considered as an example of the first of these tests. The citation of the Three Divine Persons as witnesses, appears to render Clemens Alexandrinus and Tertullian (of the same century with Theophilus) examples of the second, and as such contributors to
https://archive.org/details/lettertoclergyof00burg/page/28/mode/2up
that distinct fragment of the verse :—And the three are one, or, And these three are one. In Basil we have the assertion of unity, but not the express connumeration of the Three
. In Theophilus we have the Three, but not the assertion of unity. In the Symbolum Antiochenum, Gregory, the Nomocanon, Pseudo-Athanasius, Maximus, &c. we have both the connumeration and the assertion.
François Xavier Schouppe (1823-1904)
https://books.google.com/books?id=zDsuAQAAIAAJ&pg=PA310