Hadith are traditions relating to the words and deeds of Muhammad. Hadith collections are regarded as important tools for determining the Sunnah, or Muslim way of life, by all traditional schools of jurisprudence.
A hadith was originally an oral tradition relevant to the actions and customs of the Islamic prophet Muhammad. Starting with the first Fitna of the 7th century, those receiving the hadith started to question the sources of the saying. This resulted in a list of transmitters, for example “A told me that B told him that Muhammad said”. This list of the chain of testimony by which a hadith was transmitted is called an Isnad. The text itself came to be known as Matn. The hadith were eventually recorded in written form, had their Isnad evaluated and were gathered into large collections mostly during the reign of Umar II (bin Abdul Aziz, grandson of Umar bin Khattab 2nd Caliph) during 8th century, something that solidified in the 9th century. These works are still today referred to in matters of Islamic law and History.
The overwhelming majority of Muslims consider hadith to be essential supplements to and clarifications of the Qur'an, Islam's holy book. In Islamic jurisprudence, the Qur'an contains many rules for the behavior expected of Muslims. However, there are many matters of concern, both religious and practical, on which there are no specific Qur'anic rules. Muslims believe that they can look at the way of life, or sunnah, of Muhammad and his companions to discover what to imitate and what to avoid. Muslim scholars also find it useful to know how Muhammad or his companions explained the revelations, or upon what occasion Muhammad received them. Sometimes this will clarify a passage that otherwise seems obscure.
Hadith are a source for Islamic history and biography. For the vast majority of devout Muslims, authentic hadith are also a source of religious inspiration. However, some contemporary Muslims argue that the Qur'an alone is sufficient. Examples of such Muslims groups are Tolu-e-Islam (Resurgence of Islam), Free Minds, and United Submitters International. Muslims who take the "Qur'an alone" viewpoint are regarded as deviant by mainstream Muslim scholars, and by the vast majority of Muslims. Hadith-trusting Muslims argue that many Qur'anic instructions are impossible to fulfill without guidance from the ahadith. (The Qur'an does not, for example, specify how many prayer cycles constitute fulfillment of each of the daily prayers). It is also important to note that most Muslims claim that the Qur'an cannot be explained or read with understanding which is why the Hadith is referred to as the "second source" of Islam. While the Qur'an states "We have made it (the Qur'an) easy to understand and in your own tongue (language) may you take heed." (Qur'an 44:58), there are great debates between Muslims regarding the views stated in the Qur'an, and those stated in the Hadith.