The Parable of the Three Rings, which attempts to settle the question of which of the three rival religions is the authentic and true religion, probably originated in the eleventh-century, and is found in a developed form in the Jewish collection, Schebet Jehuda, composed in the fifteenth century. Etienne de Bourbon [died c.1261] developed a version; another version is the Dit du vrai anneau composed between 1270-1294. In the Gesta Romanorum, a source for many writers such as Chaucer, Boccaccio, and Shakespeare, which was probably composed between the end of the thirteenth and the beginning of the fourteenth, “One son (Judaism) inherits the Promised Land, one (Islam) worldly treasures and the third (Christianity) healing faith”. Boccaccio in the Decameron [I.3] develops the story further: Saladin tries to trick a Jew called Melchisedech into lending him money. “The Jew tells the Parable of the Three Rings, and the three virtuous sons, each of whom thinks he has the true ring. It proves impossible to tell the rings apart, and so the story concludes that it is impossible to determine which of the three religions is the true one.” 
Gotthold Lessing borrowed this story from Boccaccio and incorporated it into his play, Nathan the Wise [written in 1778–79] — a work that exemplifies the Enlightenment’s openness to the Other, and its universalism and tolerance. The two themes “” “it suffices to be a man” and “be my friend” “” run through the play and give it its humanity. Preaching friendship among the three monotheistic religions (Saladin, the great Muslim leader who defeated the Christian Crusaders, is one of the three main characters), Lessing recounts the allegory of the father (God) who gives each of his three sons (representing Islam, Christianity, and Judaism) a ring (representing religion):
The judge went further on to say:
If you will have my judgment, not my advice,
Then go. But my advice is this:
You take the matter as it stands.
If each one had his ring straight from his father,
So let each believe his ring the true one.
‘Tis possible your father would no longer tolerate
The tyranny of this one ring in his family,
And surely loved you all””and all alike,
And that he would not two oppress
By favouring the third.
Now then, let each one emulate in affection
Untouched by prejudice. Let each one strive
To gain the prize of proving by results
The virtue of his ring, and aid its power
With gentleness and heartiest friendliness,
With benevolence and true devotedness to God;
And if the virtue of the ring will then
Have proved itself among your children’s children,
I summon them to appear again
Before this judgment seat,
After a thousand thousand years.
Here then will sit a judge more wise than I,
Who will pronounce. Go you.
So said the modest judge. 
Many writers used the theme of Saladin converting or almost converting to Christianity as a means to criticize what they thought were the abuses in the Christian Church, a Medieval equivalent of the eighteenth century craze of exotic visitors observing and mocking European customs. Gilles de Corbeil [died first quarter 13th Century], for example, in his poem, Ierapigra ad purgandos prelatos (roughly, “Laxative for Purging Prelates” ) a satire in nine books and 5,929 verses, targets Guala Bicchieri, a cardinal and papal official, and satirizes rather ferociously the abuses prevalent among ecclesiastical officials. In the poem, Saladin has instructed himself in the Christian religion, and is about to convert but decides against it being put off by the behaviour of the clergy, who were wallowing in lust, dishonesty, envy, wickedness and pillage. In yet other accounts, Saladin criticises the coarseness of the Christians; their uncharitable attitude to the poor; the offertory; “the worship of the Pope”; and so on.
 Jubb, op.cit., p. 96.
 Gotthold Ephraim Lessing, Nathan the Wise, trans. William Jacks, Glasgow: James Maclehose & Sons, 1894, p. 134.
 A Salerno glossary explains yerapigra literally as “sacred and bitter medicine,” sacrum amarum, from Greek á¼±ÎµÏÏŒÏ‚, often used for a special pharmacological recipe, and Ï€Î¹ÎºÏÏŒÏ‚ masculine (pikrÃ³s) feminine Ï€Î¹ÎºÏÎ®, neuter Ï€Î¹ÎºÏÏŒ, =bitter.
To be continued.