Muhammad al-Bukhari
The work of "ʻilm al-ḥadīth" criticism of hadith is found in major collections of hadith of the third century of Islam—which for Sunni Muslims is "Kutub al-Sittah". ("Kutub al-Sittah", or "The six books", includes Sahih al-Bukhari of Muhammad al-Bukhari, mentioned above, but also Sahih Muslim, Sunan Abu Dawood, Jami' al-Tirmidhi, Sunan Al-Nasa'i, and Sunan ibn Majah.)