WHEN DID PALESTINIANS FORM A NATIONAL IDENTITY

Could you please cite to your sources in answering this question, as it is subject to a lot of controversy. The question is straight forward. When did Palestinians form a national identity. The earlier source I could find is 1921 with the appointment of the Al-Husseini the Grand Mufti of Palestine. Is there a earlier point than this? My understanding is they did not take on the name Palestinian until 1964?