Saint Francis of Assisi converted the sultan to the Catholic faith
from the Little Flowers of St. Francis
St. Francis, urged by zeal for the faith of Christ and by a wish to suffer martyrdom, took with him twelve of his most holy brothers, and went one day beyond the sea with the intention of going straight to the Sultan of Babylon. They arrived in a province belonging to the Saracens, where all the passes were guarded by men so cruel, that none of the Christians who went that way could escape being put to death. Now it pleased God that St. Francis and his companions should not meet with the same fate; but they were taken prisoners, and, having been bound and ill-treated, were led before the Sultan. St. Francis stood before him, and inspired by the Holy Spirit he preached most divinely the faith of Christ; and to prove the truth of what he said, professed himself ready to enter into the fire. Now the Sultan began to feel a great devotion towards him, both because of the constancy of his faith, and because he despised the things of this world (for he had refused to accept any of the presents which he had offered to him), and also of his ardent wish to suffer martyrdom. From that moment he listened to him willingly, and begged him to come back often, giving both him and his companions leave to preach wherever they pleased; he likewise gave them a sign of his protection, which would preserve them from all molestation.
At last St. Francis, seeing he could do no more good in those parts, was warned by God to return with all his brothers to the land of the faithful. Having assembled his companions, they went together to the Sultan to take leave of him. And the Sultan said to him: "Brother Francis, most willingly would I be converted to the faith of Christ; but I fear to do so now, for if the people knew it, they would kill both me and thee and all thy companions. As thou mayest still do much good, and I have certain affairs of great importance to conclude, I will not at present be the cause of thy death and of mine. But teach me how I can be saved, and I am ready to do as thou shalt order." And St. Francis answered: "My lord, I will take leave of thee for the present; but after I have returned to my own country, when I shall be dead and gone to heaven, by the grace of God, I will send thee two of my monks, who will administer to thee the holy baptism of Christ, and thou shalt be saved, as the Lord Jesus has revealed to me; and thou in the mean time shalt free thyself from every hindrance, so that, when the grace of God arrives, thou be found well disposed to faith and devotion."
The Sultan promised so to do; and did as he had promised. St. Francis returned to the venerable college of his saintly brethren, and after a few years ending his mortal life, he gave up his soul to God. The Sultan, having fallen ill, awaited the fulfillment of the promise of St. Francis, and placed guards in all the passes, ordering them if they met two brothers in the habit of St. Francis to conduct them immediately to him. At the same time St. Francis appeared to two of his monks, and ordered them without delay to go to the Sultan and save his soul, according to the promise he had made him. The monks set out, and having crossed the sea, were conducted to the Sultan by the guards he had sent out to meet them. The Sultan, when he saw them arrive, rejoiced greatly, and exclaimed, "Now I know of a truth that God has sent His servants to save my soul, according to the promise which St. Francis made me through divine revelation." Having received the faith of Christ and holy baptism from the brothers, he was regenerated in the Lord Jesus Christ; and having died of his disease, his soul was saved, through the merits and prayers of St. Francis.