The primary source of Islamic law is Divine Revelation. It has been given to humankind by the Prophet Muhammad (SAW) in 2 kinds. One is the Quran, the direct word of Allah (SWT), and the other is the Sunnah or the teachings of the Prophet (SAW). The Prophet (SAW) always acted according to the instructions of Allah (SWT).
Hadith which is usually applied also for Sunnah, is oral custom relating to the words and deeds of the Muslim prophet Muhammad saw. Lingually the word hadith means that which is fresh from amongst things or some informations communicated either in a micro amount or large. In Islamic nomenclature, the term hadith refers to report about the statements or actions of Muhammad, or about his implied approval of something stated or done in his presence.
The Quran and the Sunnah are complimentary. The meaningful of the Quran is in general in nature. The Sunnah gets it specified and particular. The Sunnah explains the instruction manual of the Quran. The Quranic injunction is sometimes implicit and the Sunnah gets in explicit by providing necessary components and items.
According to Islamic jurists, the Sunnah is second to fard. Fard means something is obligatory and it must be done; to neglect it without any excuse is a sin. The Sunnah is divided into confirmed (Sunnah muakkadah) and optional (Sunnah ghair muakkadah).
A hadith consists of two aspects: the text of the report (matn) containing the actual narrative; and the chain of narrators (isnad, or sanad), which documents the route by which the report has been transmitted.
Hadith are generally categorized as sahh (sound, authentic), da’f (weak), or mawd’ (fabricated). Other classifications used also include: hasan (good), which refers to an otherwise sahh report suffering from minor deficiency, or a weak report strengthened due to numerous other corroborating reports; and munkar (ignored) which is a report that is rejected due to the presence of a solitary and generally unreliable transmitter. Both sahh and hasan reports are considered acceptable for usage in Islamic legal discourse. Classifications of hadith may also be based upon the scale of transmission. Reports that pass through many reliable transmitters at each point in the isnad up until their collection and transcription are known as mutawtir.
Muslims who accept hadith believe that trusted hadith are in most cases the words of Muhammad and not the word of God. Hadith Qudsi forms a partial exception; these (few) hadith are said to recount divine revelations given to Muhammad but not included in the Qur’an. However, the words (as opposed to the substance) are believed to be Muhammad’s own, and not divine. Muslims also use the Ahadith to interpret parts of the Qur’an when verses are not clear or even when verses are clear to achieve an in-depth understanding.