Inimitability of the Quran (or "I'jaz") is the belief that no human speech can match the Quran in its content and form. The Quran is considered an inimitable miracle by Muslims, effective until the Day of Resurrection—and, thereby, the central proof granted to Muhammad in authentication of his prophetic status. The concept of inimitability originates in the Quran where in five different verses opponents are challenged to produce something like the Quran: "If men and sprites banded together to produce the like of this Quran they would never produce its like not though they backed one another." So the suggestion is that if there are doubts concerning the divine authorship of the Quran, come forward and create something like it. From the ninth century, numerous works appeared which studied the Quran and examined its style and content. Medieval Muslim scholars including al-Jurjani (d. 1078) and al-Baqillani (d. 1013) have written treatises on the subject, discussed its various aspects, and used linguistic approaches to study the Quran. Others argue that the Quran contains noble ideas, has inner meanings, maintained its freshness through the ages and has caused great transformations in individual level and in the history. Some scholars state that the Quran contains scientific information that agrees with modern science. The doctrine of miraculousness of the Quran is further emphasized by Muhammad's illiteracy since the unlettered prophet could not have been suspected of composing the Quran.

What term indicates that the contents of the Quran cannot be reproduced in speech?