Ya'qub ibn Ibrahim al-Ansari (Arabic: يعقوب بن إبراهيم الأنصاري, romanized: Yaʿqūb ibn Ibrāhīm al-Anṣārī), better known as Abu Yusuf (Arabic: أبو يوسف, romanized: Abū Yūsuf) (729–798) was a student of jurist Abu Hanifa[3] (d.767) who helped spread the influence of the Hanafi school of Islamic law through his writings and the government positions that he held.
[5] While much of what is known of his early childhood relies on sometimes contradictory anecdotal evidence, it has been verified that he studied religious law and traditions in Kufa and Medina under a number of scholars including Abu Hanifa, Malik b. Anas, al-Layth b. Sa'd and others.
According to one story, Abu Yusuf was able to provide sound advice pertaining to religious law to a government official who rewarded him generously and recommended him to the caliph, Harun al-Rashid.
[4] While at the time it was meant as an honorific title, the Caliph frequently consulted Abu Yusuf on legal matters and financial policy and even bestowed upon him the ability to appoint other Qadis in the empire.
[4] During his lifetime, Abu Yusuf created a number of literary works on a range of subjects including Islamic jurisprudence, international law, narrations of collected traditions (ahadith), and others.
The exception is his book entitled Kitāb al-Kharāj, a treatise on taxation and financial issues facing the empire written at the request of the caliph, Harun al-Rashid.
[6] The Islamic empire was at the height of its power at the time of his writing and in his treatise, he sought to advise the caliph on how to appropriately conduct financial policies in accordance with religious law.