Irenaeus

For this reason, also, Philip, when he had discovered the eunuch of the Ethiopians' queen reading these words which had been written: "He was led as a sheep to the slaughter; and as a lamb is dumb before the shearer, so He opened not His mouth: in His humiliation His judgment was taken away; " and all the rest which the prophet proceeded to relate in regard to His passion and His coming in the flesh, and how He was dishonoured by those who did not believe Him; easily persuaded him to believe on Him, that He was Christ Jesus, who was crucified under Pontius Pilate, and suffered whatsoever the prophet had predicted, and that He was the Son of God, who gives eternal life to men. And immediately when [Philip] had baptized him, he departed from him. For nothing else [but baptism] was wanting to him who had been already instructed by the prophets: he was not ignorant of God the Father, nor of the rules as to the [proper] manner of life, but was merely ignorant of the advent of the Son of God, which, when he had become acquainted with, in a short space of time, he went on his way rejoicing, to be the herald in Ethiopia of Christ's advent. Therefore Philip had no great labour to go through with regard to this man, because he was already prepared in the fear of God by the prophets.