ijmāʿ, in Islamic law, the universal and infallible agreement of either the Muslim community as a whole or Muslim scholars in particular. The consensus—sometimes justified through a saying from the Hadith (traditions of the sayings and actions of Muhammad), “My people will never agree in an error”—constitutes one of the sources of Islamic jurisprudence, uṣūl al-fiqh.
In Muslim history, ijmāʿ has always referred to consensuses reached in the past, near or remote, and never to contemporaneous agreement. It is thus a part of traditional authority. Ijmāʿ also has come to operate as a principle of toleration of different traditions within Islam. It thus allows, for example, the four legal schools (madhhabs) equal authority and has probably validated many non-Muslim practices taken into Islam by converts.