Augustine of Hippo, on Acts 1:1

“The former treatise I made, O Theophilus, of all things which Jesus began to do and to teach,”

“This statement teaches us that, previous to this, Luke had written one of those four books of the gospel which are held in the loftiest authority in the church. At the same time, when he tells us that he had composed a treatise of all that Jesus began both to do and teach until the day in which he commissioned the apostles, we are not to take this to mean that he actually has given us a full account in his Gospel of all that Jesus did and said when he lived with his apostles on earth. For that would be contrary to what John affirms when he says that there are also many other things which Jesus did, and if they should all be written down, the world itself could not contain the books. And besides, all agree that many things are narrated by the other Evangelists, which Luke himself does not mention in his history. The sense, therefore, is that he wrote a treatise of all these things to the extent that he made a selection out of the whole mass of materials for his narrative and introduced those facts which he judged fit and suitable to fulfill the duty laid upon him.”

Imported from an open dataset — not yet checked against the printed edition.