According to this documentary, OSAS originated with the Gnostics, was constantly being refuted by the early church, and was unknown in the Church until the 5th century when Augustine, Bishop of Hippo, a former Gnostic, brought it into the church.
00:01:36 "Believers in OSAS invariably take the high ground historically as though they're defending the historic faith. This is incredibly dishonest. That's because before Augustine's novel teachings in the early 5th century, absolutely no one in the early church believed in once saved always saved. I know of no patristic scholar or church historian who disputes that fact."
00:03:22 "The early church fathers actually warned against the idea of OSAS because that doctrine was not found within any Christian churches at the time; it was found among the Gnostics. ... in their refutations of the Gnostics, they would mention how these Gnostics believed that you could never fall away from the faith..."
00:01:36 "Believers in OSAS invariably take the high ground historically as though they're defending the historic faith. This is incredibly dishonest. That's because before Augustine's novel teachings in the early 5th century, absolutely no one in the early church believed in once saved always saved. I know of no patristic scholar or church historian who disputes that fact."
00:03:22 "The early church fathers actually warned against the idea of OSAS because that doctrine was not found within any Christian churches at the time; it was found among the Gnostics. ... in their refutations of the Gnostics, they would mention how these Gnostics believed that you could never fall away from the faith..."