Abu Abdullah Jafar bin Muhammad was born, according to Yaqubi (2nd vol., p. 381) in 80/699 at Medina. Ibn Khallikan (1st vol., p. 327) and others also determine his birth from the event of Amm al-Juhaf (the year of the flood) in Mecca, which according to Tabari (2nd vol., p. 320) occured in 80/699.
According to the Arabic lexicon, jafar means "stream". His father had referred to him "the best of all mankind" and "one in charge of the family of Muhammad" (qaim al-Muhammad). He is also known by the titles of al-Sadik (trustworthy), al-Sabir(patient), al-Tahir (pure one) and al-Fazil (excellent one).
For the first 14 years of his life, he was brought up under the care of his grandfather, Zayn al-Abidin. He observed the latter's acts of clarity, his love for long series of prostrations and prayers as well as the withdrawal from politics. He spent 23 years under his father, and assumed the Imamate at the age of 34 years.
His fame for religious learning was great. According to Yaqubi, it was customary for scholars, who related anything from Jafar Sadik, used to say: "the Learned One informed us". Even Malik bin Anas (d. 179/795), the famous jurist of Medina, is reported to have said when quoting Jafar Sadik's traditions: "The thiqa (truthful) Jafar bin Muhammad himself told me that ..." Abu Hanifah (d. 150/767) is also reported to have been Imam's pupil for two years. Shibli Nomani writes in "Sirat-i Numan" (pp. 28-29) that, "Abu Hanifah learned a great deal from Imam Baqir's son, Jafar Sadik also, which fact is generally mentioned in the history books. Ibn Taimiyyah, however, denies this on the ground that Abu Hanifah and Jafar Sadiq were contemporaries and equals, which ruled out the probability of the former being the latter's pupil. But I consider this sheer impudence and lack of comprehension on Ibn Taimiyyah's part. For all his greatness as an original thinker and master of fiqah, Abu Hanifah could not compare in learning with Imam Jafar Sadiq. The Ahl-al-Bait were the fountain-head of Hadith and fiqah and, in fact, all religious learning. `The master of the house knows best what is in it', to quote a well-known Arabic saying." Abu Hanifah also attended many lectures of Jafar Sadik. Inspite of many differences of opinion with the Imam, he was deeply influenced by him. Donaldson goes even beyond saying that he was one of Jafar Sadik's pupils, vide "The Shiite Religion" (London, 1933, p. 132)
The house of Jafar Sadik in Medina took a real shape of a regular academy, where a galaxy of talented scholars of jurisprudence, traditions, philosophy, exegesis and theology attended the studies. It was perhaps the first academy in Islam in respect of Islamic ideology which Jafar Sadiq founded in Medina. The concourse of the varied minds in Medina gave an impetus to the cultivation of science and literature, where a stream of unusual intellectual activity flowed towards other Islamic states, and soon led to the growth of philosophical tendencies among the Muslims.
The period of Jafar Sadik saw the most crucial time of Islamic history, both in political and religious spheres. We will cast a rapid glance at the political upheavals of the period under review. Jafar Sadik witnessed 3 years of the rule of Abdul Malik, the Umayyad ruler, 9 years and 8 months of Walid bin Abdul Malik, 3 years and 3 months of Suleman, 2 years and 5 months of Umar bin Abdul Aziz, 4 years and 1 month of Yazid bin Abdul Malik, 10 years of Hisham bin Abdul Malik, 1 year of Walid bin Yazid and 6 months of Yazid bin Walid; till finally the empire of the Umayyads ended in 132/750 by the Abbasids. It implies that the period of Jafar Sadik may be said to consist of two parts. During the first part, while the Umayyads were in power, the Imam was engaged in teaching quietly at home in Medina. During the second part, the Abbasids were in power after the fall of the Umayyads of Damascus in 132/750. The Umayyad empire was overthrown by the huge upheaval lead by Abu Muslim Khorasani, and the Abbasid caliphate came into existence with Abul Abbas as- Saffah as the first caliph. Hence, Jafar Sadik also witnessed the rule of as-Saffah (132-136/750-754) and Mansur (136-158/ 754-775). In sum, Jafar Sadik absolutely remained away from political arena.