The resurrection accounts of Jesus were not only from Christian writers; they were also from non-Christian writers.
Tacitus, the Roman historian, who was born between AD 52 & 54 wrote about the reign of Nero. “Nero…..punished with the utmost refinements of cruelty a class of men, loathed for their vices, whom the crowd styled Christians. Christus, from whom they got their name, had been executed by sentence of the procurator Pontius Pilate….”
About A.D.52, a writer named Thallus wrote a history of Eastern Mediterranean world. The work has been lost but excepts from it have been used by another historian, Julius Africanus, who lived in the early part of the third century. Julius Aficanus describes the earthquake and the darkness that appeared suddenly during the death of Christ as an eclipse of the sun.
Not only was the resurrection accounts of Jesus recorded in the Bible, it was also substantiated outside the Bible.
A first century Jewish historian Josephus wrote, “He was the Christ. And when Pilate, at the suggestion of the principal men amongst us, had condemned him to the cross, those that loved him at the first did not forsake him; for he appeared to them alive again the third day…”