One piece of evidence showing that Sundiata was not a devout Muslim is his reliance on magic. Islam forbids magic, even just reading the horoscope or palm reading. An example of Sundiata's use of magic came in a battle with Soumaoro. Sundiata was told that he could defeat his enemy if he used an arrow that had been tipped with a magical rooster's claw.
He wasn't a Muslim so...yea.