Kassig has become a devout Muslim, prays five times a day and fasts twice a week, and has changed his name to Abdul Rahman. Henin, who shared a cell with Kassig:
Peter converted shortly after he was captured. When I first met him [in December last year], he was already introducing himself as Abdul Rahman, which was the name he decided to take right after his conversion
He says the conversion is not due to being captured by ISIS.