...but to answer your question more precisely, there are first-century tombstones bearing prayers and commitments to atonement for the dead, right under the still-living apostles' noses in Jerusalem and Antioch. If they had a problem with the practice, it's awfully strange that there is no biblical record of their opposition to it.
So the answer is that the doctrine was practiced in the early church in the time of the apostles exactly where the apostles preached.
"there are first-century tombstones bearing prayers and commitments to atonement for the dead"
Just because they were doing it in the first century doesn't make it right. There were a lot of things being done wrong by Christians and Paul addressed some of them but I don't think it would have been possible for him to have addressed them all.
You waste your time arguing with Catholic haters such as RoadTest appears to be.