It is a mistake to assume, as is frequently done, that Sunni Islam emerged as normative from the chaotic period following Muhammad's death and that the other two movements simply developed out of it
أركان الإسلام
أهمية العرف في الإسلام, وقصدنا من هذا تنبيه المفتين والباحثين على أهمية معرفة
the taking of later and often highly ideological sources as accurate historical portrayals — and in part on the fact that the overwhelming majority of Muslims throughout the world follows now what emerged as Sunni Islam in the early period
used the other to define itself more clearly and in the process to articulate its doctrinal contents and rituals