Saracen vs children of Ishmael

Saracen

noun
  • A type of six-wheeled armoured personnel carrier. 

  • A member of a nomadic people from the Sinai near the Roman province of Arabia in the early centuries CE, who were specifically distinct from Arabs. 

children of Ishmael

How often have the words Saracen and children of Ishmael occurred in a corpus of books? (source: Google Ngram Viewer )