Hadith are divided into two groups:
- hadith qudsi ("sacred Hadith"), in which God Himself is speaking in, as it were, a complementary revelation through the Prophet (PBUH), and
- hadith sharif ("noble Hadith"), the Prophet's own acts and utterances.
The most famous collections of Hadith are the Sahih ("the Authentic") of Muhammad Ibn Ismail al-Bukhari (d. 256/870) and the Sahih of Abu-I-Husayn Muslim ibn al-Hajjaj (d. 261/875; usually called "Muslim"). These two Sahihs, or as-Sahihan (the Arabic dual of Sahih), are the most authoritative of the six well-established collections. The others are those of Abu Dawud (d. 261/875), at-Tirmidhi (d. 279/892), an Nasai (d. 303/915), and Ibn Maja (d. 273/886). These make up the "six books" (al kutub as-sittah); however, equally famous are the Muwatta of Malik ibn Anas, the first collection ever written down, and the Musnad of Ibn Hanbal.
Many other Hadith are found in such books as the Hilyat al-Awliya ("Adornment of the Saints") of Abu Nu'aym. There are also a number of small collections, the most notable being the Forthy Hadith of Nawawi, which contain those sayings generally considered to be of the greatest importance and the essential minimum for a Muslim's education.
The collections of Bukhari and Muslim were scrupulously compiled in the first century and a half of Islam, their authenticity being and a half of Islam, their authenticity being proved by the criterion which the people of the time found most valid, namely an authoritative isnad, or chain of transmission. The method was based on the assumption that it was unthinkable for God-fearing men to lie about matters which they held sacred, each human link in the chain vouchsafed the others.
If there were persons in the isnad whose integrity could be doubted for any reason, however small the authenticity of the Hadith was to that extend weakened; conversely if there existed several distinct accounts and varied chains of transmission for a single Hadith, its authenticity was to that extent strengthened.
Islam views the actions of a Divine Messenger as providential and unlimited in their inner nature. Therefore it is with the authority of the Holy Quran which states: "You have a noble example God's Messenger" (33:21), that Islam bases its Sunnah upon the Hadith in addition to the Holy Quran.
If the Hadith were to play such an important role in the development of an entire civilisation, their scope must be vast. Throughout the centuries, as Islam evolved, it searched cut the traditions of the Prophet's (PBUH) life to guide the faithful.
The Hadith were accorded the role of basis of law in Islamic jurisprudence by the universally accepted methodology of ash-Shafii. It then became inevitable that as Islam unfolded in history, the need for the tangible support which Hadith could provide for intellectual and cultural developments called forth the "missing" or "unspoken" Hadith that were now required. if in the first centuries the standard by which Hadith were measured was that of an impeccable isnad, the growing needs of an expanding Islam of later times added de facto another, one of verisimilitude in the eyes of a developed and sophisticated religious community.
There are so-called "Hadith" and Sunnah" which are patently, or pointlessly false, such as the common story that the Prophet (PBUH) went into rages upon seeing a shape resembling a cross, and shattered crosses whenever he found them.
This is in such contradiction to the Prophet's nature that it is easy to see it as a zealot fable substituting human pettiness for Prophetic rigor. It is not true, nor does it add any depth or strength to what is in fact true.