Sudanese sultans rather than Egyptian rulers granted al-Tunisï his travel authority

Evidence

What authority gave Muhammad al-Tunisï the ability to travel around the vast regions of Därfür and document the behavior of its inhabitants? Unlike Selim Qapudan and al-Tahtawï, Muhammad al-Tunisï did not travel to the Sudan under the orders of the Egyptian ruler. Once situated there, however, he did gain the permission of the sultan of Därfür, to travel around the region of Jebel Marra, permission that he carried with him, signed and sealed, throughout his journeys. This authority, and the guards that came with it, shielded him from violence and gave him a layer of protection when he encountered hostile tribes in the market town of Numliyya. — Eve M. Troutt Powell, A Different Shade of Colonialism_…, 165