Ja'far ibn Muhammad ibn Ali al-Sadiq (702–765), commonly known as Ja'far al-Sadiq - "Ja'far the Truthful" was the 8th Muslim Shia scholar, jurist and theologian of the century. He was the founder of the Jafarite school of Islamic jurisprudence and the sixth Imam of the Twelver and Ismaili denominations of Shia Islam. Traditions (hadith) recorded from al-Sadiq and his predecessor Muhammad ibn Ali al-Baqir are considered more numerous than all the hadiths preserved from the Islamic prophet Muhammad and other Shia imams combined.
Among other theological contributions, he developed the doctrine of nass (the divinely inspired appointment of each imam as a previous imam) and isma (the infallibility of imams), as well as the doctrine of taqiyyah (religious pretense in the course of prosecution).
Al-Sadiq is also important to the Sunnis as a jurist and hadith transmitter, and teacher of the Sunni scholars and imams Abu Hanifa al-Numan and Malik ibn Anas, who founded the Hanafi and Maliki schools of the Sunnis, jurisprudence, respectively.
Al-Sadiq also figures prominently in the initiatory chains of many Sufi orders. A wide range of religious and scientific works are attributed to him, although not a single work written by al-Sadiq survives.
Ja'far al-Sadiq was born around 700 CE, possibly 702. He was about thirty-seven years old when his father, Muhammad al-Baqir, died after appointing him as the next imam. As the sixth Shia Imam, al-Sadiq kept aloof from the political conflicts that engulfed the region, dodging requests for support he received from the rebels.
He became a victim of persecution by the Abbasid Caliphs and was eventually poisoned, according to Shiite sources, at the instigation of Caliph al-Mansur. The question of succession to the throne after al-Sadiq's death divided the early Shia community. Some considered the next imam to be his eldest son Ismail ibn Jafar, who predeceased his father. Others accepted the imamate of his younger son and brother Ismail Musa al-Kazim. The first group became known as the Ismailis, while the second and larger group was called the Jafari or Twelvers.
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