Who or what is "Zaabalwi"?

The story "Zaabalwi" by Nagub Mahfouz is about a narrator's quest for Zaabalwi. The story takes place in Cairo and the narrator looks everywhere to find the mysterious character Zaabalwi. The narrator is looking for Zaabalwi because he has a disease, which no doctor can cure, and he believes Zaabalwi can heal him. The people of Cairo refer to Zaabalwi as a saint, who possess physical healing, and religious salvation.
The narrator first hears about Zaabalwi from his father. His father says "he's a true saint of God, a remover of worries and troubles, were it not for him I would have died mi…