The ijazah system is historically bound up with the broader Islamic science of hadith criticism, since the reliability of a reported saying of the Prophet was assessed largely through scrutiny of its isnad, the named chain of transmitters carrying the report back to its source, the same chain of personal transmission an ijazah documents for a body of teaching more generally. This gave the system unusual rigor for its time, since a transmitter's individual reputation for honesty and accuracy became directly load bearing for the credibility of what they transmitted, whether a legal ruling, a hadith, or a license to teach.
The rise of modern university style institutions across much of the Muslim world introduced degree granting structures that operate alongside, and in some contexts have partly displaced, the traditional ijazah system, though the practice remains very much alive in traditional religious education, including Quranic recitation certification, hadith study circles, and Sufi orders, where an ijazah continues to carry weight distinct from, and in some communities considered more significant than, a modern academic credential covering similar material. Historians of Islamic education have used surviving ijazah documents, preserved in manuscript libraries across the Middle East, North Africa and South Asia, to reconstruct genealogies of scholarly transmission stretching back many centuries.