There's no indication from contemporary sources at that time that this was a battle between Islam and Christendom. That's something that was fabricated later. Ah, I wonder why. The narrative began in a book called Decline and Fall of the Roman Empire by Edward Gibbon, released in 1776. In the book, Gibbon argues that the Roman Empire fell due to embracing Christianity, which is not a position that most historians agree with. Leaving that central thesis aside, his book also serves as the jumping off point for the retelling of the Battle of Tour, with his casting of Martel as a heroic leader who stopped Islam from overtaking the Western world. This was not a case of Gibbon reflecting actual history. It was him using a historical event to craft a narrative.