Summary of the story based on Beyhaqi's narration

Bozorgmehr abandoned the Zartoshtian faith and converted to the religion of Jesus (peace be upon him), stating that based on what he had read in the scriptures, the Prophet of Islam would appear, and if he found him, he would be the first to follow him. Anusharvan was very angry with Bozorgmehr's apostasy and told him that by doing so, he was causing his subjects and army to believe they were not on the right path, which could lead to both private and general rebellion. Anusharvan urged Bozorgmehr to return to the religion of his ancestors and forefathers. Bozorgmehr said, "Since I have come from darkness into light, I will not return to darkness, lest I become ignorant and senseless." Kasra threatened him with death. Bozorgmehr was not afraid of the threat and replied, "The judge I will go to is just and will neither require witnesses nor punish you, nor will he withhold his mercy from you. At the end, Kasra said to himself, "It is a pity to ruin this," and then ordered that Bozorgmehr be placed in a very dark prison cell.
The story continues in the history of Bayhaqi: After two years, they had not heard from Bozorgmehr, so they informed Kasra, saying, "He said, 'Open Bozorgmehr's prison.' People expected that Bozorgmehr would have become thin and sick after enduring the harsh and dark period of imprisonment, with minimal food and water, and that these effects would be visible on his face and body. However, they found him in excellent health, with a strong body and a healthy complexion.