Being a prisoner of war and a slave to a Turkish Ağa, he became famous and respected even by his Muslim master for his humility, steadiness in faith and benevolence.

His holy relics are claimed to be incorrupt and wonderworking; there are traditions that this saint particularly helps sick children and those who suffer from cancer.

During the war, he was taken prisoner and sold as a slave to the head of the Ottoman cavalry who lived in Ürgüp in Cappadocia (modern-day central Turkey).

Because he refused to convert to Islam, John was humiliated and tormented by the Ottoman Turks, who called him a gavur (unbeliever).

For his kind-heartedness, John earned the love and trust of the Ağa who offered to let him live as a free man in a separate house.

During the day John worked and prayed, keeping a strict fast, but when the night came, he used to go in secret to the cave-church of St. George, where he said the prayers of the All-Night Vigil.

When the Ağa returned, he described a miracle that had happened to him: whilst in Mecca, he found a steaming plate of pilau in his locked room.