Sayyidah Fusaylah bint Wathilah bin al-Asqa' (may Allah be pleased with her) said: I heard my father (Sayyiduna Wathilah bin al-Asqa', may Allah be pleased with him) say: I asked: O Messenger of Allah! What is tribalism ('asabiyyah)? He (peace and blessings be upon him) said: "Helping your people in wrongdoing."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 21076