Against The Valentinians by Tertullian
Chapter V.--Many Eminent Christian Writers Have Carefully and Fully Refuted the Heresy These the Author Makes His Own Guides.
My own path, however, lies along the original tenets of their chief teachers, not with the self-appointed leaders of their promiscuous followers. Nor shall we hear it said of us from any quarter, that we have of our own mind fashioned our own materials, since these have been already produced, both in respect of the opinions and their refutations, in carefully written volumes, by so many eminently holy and excellent men, not only those who have lived before us, but those also who were contemporary with the heresiarchs themselves: for instance Justin, philosopher and martyr; Miltiades, the sophist of the churches; Irenæus, that very exact inquirer into all doctrines; our own Proculus, the model of chaste old age and Christian eloquence. All these it would be my desire closely to follow in every work of faith, even as in this particular one. Now if there are no heresies at all but what those who refute them are supposed to have fabricated, then the apostle who predicted them must have been guilty of falsehood. If, however, there are heresies, they can be no other than those which are the subject of discussion. No writer can be supposed to have so much time on his hands as to fabricate materials which are already in his possession.