Irenaeus

As Luke was present at all these occurrences, he carefully noted them down in writing, so that he cannot be convicted of falsehood or boastfulness, because all these [particulars] proved both that he was senior to all those who now teach otherwise, and that he was not ignorant of the truth. That he was not merely a follower, but also a fellow-labourer of the apostles, but especially of Paul, Paul has himself declared also in the Epistles, saying: "Demas hath forsaken me, ... and is departed unto Thessalonica; Crescens to Galatia, Titus to Dalmatia. Only Luke is with me." From this he shows that he was always attached to and inseparable from him. And again he says, in the Epistle to the Colossians: "Luke, the beloved physician, greets you." But surely if Luke, who always preached in company with Paul, and is called by him "the beloved," and with him performed the work of an evangelist, and was entrusted to hand down to us a Gospel, learned nothing different from him (Paul), as has been pointed out from his words, how can these men, who were never attached to Paul, boast that they have learned hidden and unspeakable mysteries?