Tertullian

He professes himself to be "an apostle"-to use his own, words-"not of men, nor by man, but by Jesus Christ." Of course, any one may make a profession concerning himself; but his profession is only rendered valid by the authority of a second person.

Should you, however, disapprove of these types, the Acts of the Apostles, at all events, have handed down to me this career of Paul, which you must not refuse to accept. Thence I demonstrate that from a persecutor he became "an apostle, not of men, neither by man; " thence am I led to believe the Apostle himself; thence do I find reason for rejecting your defence of him, and for bearing fearlessly your taunt.