It is no secret that some scholars of Muslim world have tried to give the credit of “Doctrines of Fiqh” to Imam Shafei.
Anyway, enough said on this subject. A few scholars with help from their imagination have gone even farther to the age of Rasul Allah (S) and have credited a companion, Moaz Ibn Jabal, with the discovery. However, the brilliant author of Aunul Maabud, Muhammad Ashraf Ibn Ali, while quoting Jozeqani has labeled this reference as a fake tradition.1
In addition, Qazi Abdul Jabbar has said the same thing on page 200 of his book, Al Mughni, vol 7. For further discussion see Al-Ahkam page 976, by Ibn Huzm Undlusi; Meezan Ul-Etidal page 439 by Zehi; Taqreeb Ut Tahzeeb vol 1 page 142 by Ibn Hajr Asqalani. And it would be very useful to study pages 39 to 42 of a very fine book, Al-Ijtihad Wa Usula wa Ahkama by Sayed Muhammad Bahar Ul-Uloom.
Anyway, different people have different things to say. But the fact of the matter is that the beneficiaries of the rivers of knowledge and wisdom of our Aimma (as) have done a commendable job of introducing the concept of Ijtihad.
The famous researcher, Allama Sayed Hasan Sadr, writes on Page 310 in his most precious book, Tasees Ush-Shia Al-Uloom Ul-Islam: The pupils, who attended the thought provoking lessons of our fifth and sixth Imams, learnt all about the “Doctrines of Fiqh” and then wrote extensively on this subject. The lofty treatise, Al-Alfaz wa Mubahisa, by Hasham Ibnul Hakam (died 179 AH) is a living proof. This scholar was a beneficiary of Imam As-Sadiq’s (as) teachings. The other personality with many wonderful qualities was Younas Ibn Abdur Rahman (died 208 AH) who wrote Ikhtilaf Ul-Hadeeth wa Masaila2.Before their time no one had written on this subject in such a way and consequently these books became the pioneering works and great models. Anyway, foundation had been laid down and the work continued.
In this context Ibn Nadeem (died 380 AH) who was extremely knowledgeable about books and personalities wrote:
A short time after the exceptional writings by Hasham Ibnul Hakam and Younas Ibn Abdur Rahman, a great thinker of School of Ahlul Bayt and a son of Naubakht family, Abu Sahal Ismail Ibn Ali (died 311 AH), wrote Al-khusus wal-Umoom and Abtalul Qias and made a weighty contribution to the “Doctrines of Fiqh”. After him when his talented nephew, Abu Muhammad Hasan Ibn Musa Naubakhti, took over the job of preaching, he in addition to many other books wrote Kitab Al-khusus wal-Umum and Al-khabrul Wahid and thus made a huge addition to the treasure of books on the subject of the “Doctrines of Fiqh”.