it is supported by the muratorian fragment, by the anti-marcionite prologue, by the writings of irenaeus, clement and origen in alexandria, and by the tertullian
1.1. It has already been determined that the Book of Acts was written by Luke; Acts is the second part of a two volume work: volume one (Luke) describes Jesus' ministry and passion; volume two (Acts) describes events after Jesus' ascension.
1.2. The Muratorian canon confirms the Lukan authorship of the Book of Acts: "Moreover the Acts of the Apostles are included in one book. Luke addressed them to the most excellent Theophilus, because the several events took place when he was present; he makes this plain by the omission of the passion of Peter and of the journey of Paul when he left Rome for Spain."