Islam
Classical era (750–1258)

Al-Shafi'i codified a method to determine the reliability of hadith. During the early Abbasid era, scholars such as Muhammad al-Bukhari and Muslim ibn al-Hajjaj compiled the major Sunni hadith collections while scholars like Al-Kulayni and Ibn Babawayh compiled major Shia hadith collections. The four Sunni Madh'habs, the Hanafi, Hanbali, Maliki, and Shafi'i, were established around the teachings of Abū Ḥanīfa, Ahmad ibn Hanbal, Malik ibn Anas and al-Shafi'i. In contrast, the teachings of Ja'far al-Sadiq formed the Ja'fari jurisprudence. In the 9th century, Al-Tabari completed the first commentary of the Quran, the Tafsir al-Tabari, which became one of the most cited commentaries in Sunni Islam. Some Muslims began questioning the piety of indulgence in worldly life and emphasized poverty, humility, and avoidance of sin based on renunciation of bodily desires. Ascetics such as Hasan al-Basri inspired a movement that would evolve into tasawwuf or Sufism.

At this time, theological problems, notably on free will, were prominently tackled, with Hasan al Basri holding that although God knows people's actions, good and evil come from abuse of free will and the devil. Greek rationalist philosophy influenced a speculative school of thought known as Muʿtazila, who famously advocated the notion of free-will originated by Wasil ibn Ata. Caliph Mamun al Rashid made it an official creed and unsuccessfully attempted to force this position on the majority. Caliph Al-Mu'tasim carried out inquisitions, with the traditionalist Ahmad ibn Hanbal notably refusing to conform to the Muʿtazila idea that the Quran was created rather than being eternal, which resulted in him being tortured and kept in an unlit prison cell for nearly thirty months. However, other schools of speculative theology – Māturīdism founded by Abu Mansur al-Maturidi and Ash'ari founded by Al-Ash'ari – were more successful in being widely adopted. Philosophers such as Al-Farabi, Avicenna and Averroes sought to harmonize Aristotle's ideas with the teachings of Islam, similar to later scholasticism within Christianity in Europe and Maimonides ' work within Judaism, while others like Al-Ghazali argued against such syncretism and ultimately prevailed.

This era is sometimes called the " Islamic Golden Age ". Islamic scientific achievements spanned a wide range of subject areas including medicine, mathematics, astronomy, and agriculture as well as physics, economics, engineering and optics. Avicenna was a pioneer in experimental medicine, and his The Canon of Medicine was used as a standard medicinal text in the Islamic world and Europe for centuries. Rhazes was the first to identify the diseases smallpox and measles. Public hospitals of the time issued the first medical diplomas to license doctors. Ibn al-Haytham is regarded as the father of the modern scientific method and often referred to as the "world's first true scientist", in particular regarding his work in optics. In engineering, the Banū Mūsā brothers' automatic flute player is considered to have been the first programmable machine. In mathematics, the concept of the algorithm is named after Muhammad ibn Musa al-Khwarizmi, who is considered a founder of algebra, which is named after his book al-jabr, while others developed the concept of a function. The government paid scientists the equivalent salary of professional athletes today. Guinness World Records recognizes the University of Al Karaouine, founded in 859, as the world's oldest degree-granting university. Many non-Muslims, such as Christians, Jews and Sabians, contributed to the Islamic civilization in various fields, and the institution known as the House of Wisdom employed Christian and Persian scholars to both translate works into Arabic and to develop new knowledge.

Soldiers broke away from the Abbasid empire and established their own dynasties, such as the Tulunids in 868 in Egypt and the Ghaznavid dynasty in 977 in Central Asia. In this fragmentation came the Shi'a Century, roughly between 945 and 1055, which saw the rise of the millennialist Isma'ili Shi'a missionary movement. One Isma'ili group, the Fatimid dynasty, took control of North Africa in the 10th century and another Isma'ili group, the Qarmatians, sacked Mecca and stole the Black Stone, a rock placed within the Kaaba, in their unsuccessful rebellion. Yet another Isma'ili group, the Buyid dynasty, conquered Baghdad and turned the Abbasids into a figurehead monarchy. The Sunni Seljuk dynasty campaigned to reassert Sunni Islam by promulgating the scholarly opinions of the time, notably with the construction of educational institutions known as Nezamiyeh, which are associated with Al-Ghazali and Saadi Shirazi.

The expansion of the Muslim world continued with religious missions converting Volga Bulgaria to Islam. The Delhi Sultanate reached deep into the Indian Subcontinent and many converted to Islam, in particular low-caste Hindus whose descendants make up the vast majority of Indian Muslims. Trade brought many Muslims to China, where they virtually dominated the import and export industry of the Song dynasty. Muslims were recruited as a governing minority class in the Yuan dynasty.
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