Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "Whoever leaves obedience and separates from the jama'ah (the main body of Muslims), then dies, has died a death of Jahiliyyah. Whoever is killed under a blind banner, getting angry for tribalism, supporting tribalism and calling to tribalism, and is killed, his killing is a killing of Jahiliyyah. And whoever rebels against my Ummah, striking its righteous and its wicked, not sparing its believers and not fulfilling the covenant of those under its covenant, is not of my Ummah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 21075