کتاب الفتن · نُعیم بن حماد

The last sign of the demise of the rule of the Banu Abbas are three kings among them who succeed one another. Their names are the names of the prophets. They will not exceed them after these kings. The duration of the Banu Abbas among these three kings is forty years. If you see differences among them, and a group of Banu Hashim gathered between the two rivers, and the mandate of a man from the Banu Abbas towards the west, and the clashing of the black flags, and zeroing in the navel of the Levant, and the killing of the governor of Egypt, and the prevention of its tax, then it is a sign of the interruption of their period.