Abu Salih (may Allah have mercy on him) narrates from Sayyiduna Mu'awiyah (may Allah be pleased with him); he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever dies while there is no pledge of allegiance (bay'ah) on his neck dies the death of Jahiliyyah (pre-Islamic ignorance)."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16818