Ma'an Arabic, writing about the UNESCO vote delegitimizing the Jewish connection to the place where the Biblical Patriarchs and Matriarchs are buried, says, says as a backgrounder:
The city of Hebron is one of the oldest ancient cities that are still inhabited in the world, and stretches back more than 6,000 years. It is a holy city of heavenly religions, and became the fourth holiest Islamic city after Mecca, Medina and Jerusalem.Really? Because, since they believe UNESCO so much, Harar in Ethiopia is the fourth most holy site in Islam. Many argue Kairouan, Tunisia.
I found a discussion from Lonely Planet ten years ago where people were discussing just this issue of what the fourth holiest site in Islam is. Cities mentioned in the discussion include Harar, Najaf, Karbala, Mashad, and Nagash. Hebron isn't mentioned at all.
The only place I could find any mention of Hebron as one of the holiest Muslim cities are from Palestinian sources.
Just as the Mufti managed to inflate the importance of Jerusalem to indifferent Muslims in the 1920s because of his hatred of Jews, so are the Palestinians today doing the same to Hebron. There is only one reason they say this: to loosen the Jewish claim on lands that are historically, religiously and culturally the most important places in Judaism.