Consensus or agreement. One of four recognized sources of Sunni law. Utilized where the Quran and Sunnah (the first two sources) are silent on a particular issue. There is considerable debate concerning whose opinions are relevant for ijma. Some argue that only the opinions of scholars are relevant. Others contend that ijma includes the consensus of the laity. Most agree that the consensus of Muhammad's Companions, the people of Medina, or the family of the Prophet is authoritative. Once an ijma is established, it serves as a precedent. According to the majority of jurists, a decision based on ijma generally cannot override a statement of the Quran or the Sunnah. The binding force of ijma is based on a hadith in which the Prophet Muhammad is reported to have said, “My community will never agree on an error.” In Twelver Shiism, consensus is neither an infallible sanctioning instrument nor a source of law. Ideas of consultation (shura) and parliamentarianism are used in attempts to formulate a theory of consensus useful in the modern world.