The so-called hadiths are based on verbal reports, which were in circulation after the death of Mohammed. From the 8th century they were evaluated and collected in large collections to preserve the knowledge of the sunna of the Prophet, and are considered sacred traditions (hadith qudsi).
The traditions were finally grouped together in collections . The most important collections for Shiites are the four books (kutub arbaa). Among the Sunnis, there are the six books (al-kutub as-sitta) important.