Medieval polemicists used Jewish and Islamic scriptures to refute each other reciprocally

Evidence

The Rabbi Samuel letters, which were put into Latin only in the middle of the fourteenth century, were asserted by their translator to have long circulated in Arabic among Christians. Their originality was to interconnect the mutual verification of the Three Laws: that is to say, both Rabbinic teaching and the Qur’an confirm the truth of the Gospel, while each of them destroys the claim of the other. Islam taught the Rabbis that Jesus Christ is the Messias, while the Jews made the Muslims understand that Muhammad was neither Messias nor Paraclete. — Norman Daniel, Islam and the West, 311

Categorization

• DEFINE: The ‘Three Laws’ mutual-verification framework is a distinct medieval dialectical method worth defining clearly.
• STORYSTEM: A mind-game structure where two scriptures are deployed like opposing testimonies in court is ripe for a debate-scene or theological-thriller worldbuilding spark.
• XREF: connects to: Muslims held that Jews and Christians corrupted their scriptures; Each religion saw the other as a corruption of its own truth. — Norman Daniel, Islam and the West, 1039; Polemics could condemn a rival religion using only its own scriptures (+1 more)