As the criteria for judging authenticity grew into the six major collections of ṣaḥīḥ (sound) hadith (Kutub al-Sittah) in the third century, the science of hadith was described as having become a "mature system",Brown, Rethinking tradition in modern Islamic thought, 1996: p.83 or to have entered its "final stage".Brown, Rethinking tradition in modern Islamic thought, 1996: p.94
