During the early centuries following the death of the Prophet (Salalah Aleyhi Wa~Alehi Wassalam) Islamic scholars sought to consolidate and systematize Islamic belief and practice. One of the challenges confronting Muslim scholars was how to determine which of the many thousands of hadith attributed to the Prophet (Salalah Aleyhi Wa~Alehi Wassalam) and his companions were authentic. In the ninth century, two scholars, Muhammad b. Isma'il Bukhari (d.870) and Muslim b. al Hajjaj (d. 875), collected and sifted through the vast numbers of traditions in order to compile dictionaries containing the authentic traditions of the Prophet (Salalah Aleyhi Wa~Alehi Wassalam). Basing their decisions on the reliability of the particular transmitters, al Bukhari and al Hajjaj reduced the massive number of traditions to several thousand. In the tenth century these collections were given canonical status by the Muslim community.

In addition to these two collections, four further collections of hadith were compiled by lesser known scholars. While regarded as authentic and canonical by the Ummah, these do not have quite the same status as those of al Bukhari and al Hajjaj.

A second area of Islamic life developed at this time was the Shari 'ah, the regulations and principles upon which Islamic law is based. The four orthodox schools of law - Hanafiyyah, Malikiyyah, Shafi'iyyah and Hanbaliyyah - elaborated the rules of procedure by which particular laws could be determined. These rules were based on the Qur'an and the Sunnah and two legal principles known as qiyas and ijma'. Qiyas is the attempt through analogical reasoning to determine how the principles of the Qur'an and the Sunnah could be applied to a situation not clearly addressed through these sources. An example of such a ruling is the extension of the Qur'anic decree against market activities during the Friday congregational prayers to a general prohibition of all business activities at this time.

Ijma', meaning consensus, was based on the principle that when no clear guidance was given by the Qur'an or the Sunnah on a principle of law the consensus of the community would be sought. All four schools accept these principles as the basis of the Shari 'ah and regard each other as orthodox. They differ with regard to the particular importance each school attaches to qiyas and ijma' relative to the Qur'an and the Sunnah.

Concomitant with the systematization of the Shari'ah was the establishment of theological orthodoxy. The encounter with non-Islamic beliefs and the emergence of deviant theological views within the community itself provided the impetus for the formation of an orthodox theology. The first major challenge to Islam from within came from the Kharijiyyah, who claimed that good works as well as the profession of faith were necessary to be a true Muslim. Those who sinned without repenting forfeited their right to belong to the community of believers. Such was their strength of feeling on this issue that they violently persecuted those who disagreed with him.

The issue of the relationship between faith and works was taken up by a second group, the Mu'tazilah, who argued that the non-repentant sinner occupied a middle state between belief and non-belief. Although endeavouring to defend Islam against Hellenistic philosophy, the Mu'tazilah drew upon Hellenistic ideas in formulating their understanding of God and the relationship between God and humanity. For the Mu'tazilah, all anthropomorphic language about God was to be interpreted as purely metaphorical. Furthermore, in order to preserve the doctrine of human freedom and responsibility, God's action was interpreted in terms of necessity and duty rather than freedom. It was the denial of God's absolute freedom that was a source of concern to mainstream Islamic thinkers.

In reaction to the Mu'tazilah doctrine, two theological schools emerged in the tenth century: Ash'ariyyah and Maturidiyyah. Both schools endeavoured to elevate revelation and reduce reason as the means by which humanity acquires a knowledge of God. By arguing that there were certain truths about the nature of God which were not accessible to human reason alone these schools sought to restore the doctrine of divine omnipotence.

The establishment of broadly based forms of jurisprudential and theological orthodoxy during its early history has not prevented the emergence of anti-orthodox tendencies in more recent times. In the eighteenth century a group known as Wahhabiyyah emerged with the purpose of "purifying" Islam of non-Islamic accretions such as the worship of the saints. Integral to this project was the attempt to base Islamic law solely on the Qur'an and the Sunnah through the rejection of qiyas and ijma' as elements within the Shari 'ah. A second, unrelated group, Ahmadiyyah, was founded in India towards the end of the nineteenth century. Its leader, Mirza Ghulam Ahamd, claimed to be the Christian Messiah, the Mahdi, an avatar of Krishna and a reappearance of Muhammad. In spite of being declared heretical by the orthodox Muslim community this group has spread beyond India into other parts of Asia and from there to Europe and Africa.