Sayyiduna Thawban (may Allah be pleased with him) narrates: The Messenger of Allah (peace and blessings be upon him) said: "The Banu al-Abbas will have two banners; their top will be disbelief and their base will be misguidance. If you reach that time, do not go astray in it."
Hadith Referenceالمعجم الكبير للطبراني / باب الثاء / 1411