Tertullian

“ Chapter XXI.—The Epistle to Philemon. This Epistle Not Mutilated. Marcion’s Inconsistency in Accepting This, and Rejecting Three Other Epistles Addressed to Individuals. Conclusions. Tertullian Vindicates the Symmetry and Deliberate Purpose of His Work Against Marcion.
To this epistle alone did its brevity avail to protect it against the falsifying hands of Marcion. I wonder, however, when he received (into his Apostolicon) this letter which was written but to one man, that he rejected the two epistles to Timothy and the one to Titus, which all treat of ecclesiastical discipline. ”