کتاب الفتن · نُعیم بن حماد

If the Sufyani reached Kufa, and the agents of the family of Muhammad were killed, the Mahdi would emerge under his banner, Shuaib bin Saleh

The black flags emerging from Khorasan will descend on Kufa, and when the Mahdi appears in Mecca, the pledge of allegiance will be sent to him