Tertullian

“ Still, in these few quotations the distinction of Persons in the Trinity is clearly set forth. For there is the Spirit Himself who speaks, and the Father to whom He speaks, and the Son of whom He speaks. ”

“ Now, you who say that the Father is the same as the Son, do really make the same Person both to have sent forth from Himself (and at the same time to have gone out from Himself as) that Being which is God. If it was possible for Him to have done this, He at all events did not do it. You must bring forth the proof which I require of you—one like my own; that is, (you must prove to me) that the Scriptures show the Son and the Father to be the same, just as on our side the Father and the Son are demonstrated to be distinct ”

“ Many Scriptures Quoted in Proof of the Distinction of the Divine Persons of the Trinity.
It will be your duty, however, to adduce your proofs out of the Scriptures as plainly as we do, when we prove that He made His Word a Son to Himself. For if He calls Him Son, and if the Son is none other than He who has proceeded from the Father Himself, and if the Word has proceeded from the Father Himself, He will then be the Son, and not Himself from whom He proceeded. For the Father Himself did not proceed from Himself. ”