Christian apologists argued with Muslims within Islamic terms rather than citing Scripture

Evidence

The tradition of Trinitarian argument is well exemplified in Yahya ibn ‘Adi, who wrote in Arabic in the tenth century, and who in many ways seems to be an oriental Ramon Lull, anxious to prove the Trinity by natural reasons alone; he at least avoided the contrary mistake of citing Scripture to Muslims who consider the canonical text corrupt. — Norman Daniel, Islam and the West, 52