Commentary on the Bible, by Adam Clarke, [1831], at sacred-texts.com
Preface to the Third Epistle of John
This epistle being of nearly the same complexion with the former, and evidently written about the same time, and incontestably by the same person, it is not necessary to give it any particular preface; as the subject of the authenticity of all the three epistles has been treated already so much at large, not only in the introduction to them, but in the notes in general.
This and the preceding epistle are, by Dr. Lardner, supposed to have been written between a.d. 80 and 90. There are no notes of time in the epistles themselves to help us to fix any date, therefore all is conjecture concerning the time in which they were written: but to me it appears as likely that they were written before the destruction of Jerusalem as after; for it is scarcely to be supposed that so signal a display of the justice of God, and such a powerful argument in favor of Christianity and of the truth of Christ's predictions, could be passed unnoticed and unappealed to by any of the inspired persons who wrote after that event. However, where there is no positive evidence, conjecture is useless.