Historians accept that the earliest Christian writing probably existed around the mid 1st century CE. Our earliest documented information comes from the apostle Paul. But Christian beliefs would have obviously existed in the minds of Christians before they were written down, and even before Paul became a Christian. We have the Gospels, and although, they tell us details about the first quarter of the first century CE, which is when they report that Christianity was starting, but evidence shows that they weren't written down until well after the time period that they report on (earliest Gospel dating around 66-70 CE).

I want to know what is the earliest dating for a Christian tradition that historians accept? Again, I know they won't accept that it dates back to the life or even birth (~6 BCE) of Jesus because historians do not accept that the disciples wrote the gospels.