Elias quoted Life of the Qur'an by Mohamad Jebara
Embark on a thought-provoking journey with The Life of the Quran, a book that explores …
... followers of the Qur'an for the first time became "Muslims" in formal contrast to Jews and Christians, whereas previously there has been fluidity of identity where someone born Jewish or Christian could be a follower of the Qur'an without feeling they had converted to a new religion.
— Life of the Qur'an by Mohamad Jebara (Page 182)
??? Not doubting the author, I'm just genuinely surprised by this. Religion never fails to surprise me