Book “Khisal” by Allama Mohd Baqar Kamraie Volume 4 Page 57. Allama says, “By the end of the 4th century Hijri, Shias only had Quran, Ahadees-e-Rasool [as] and the traditions of Masoomeen which were the bases of “Hukm -e-Sharia” but when Shias started following the patterns of Aama (Ahl-e-Sunna ) writing books on Usool-e-Fiqh which were away from the traditions, they also included “Ijma and Daleel-e-Aqal” in from Ahl-e-Sunnah into Usool-e-Fiqh for Shias. When they realised that Ijma and Daleel-e-Aql are against the Maktab-e-Ahlul Bait , they got busy in doing “Taujeeh & Taweel” and started saying that from Ijmah we mean Traditions of Masoom and “Aql”. The use of “Fikr Araie” in “Masael-e-Usooli” resulted in the inclusion of Qayas in the name of “Tanqeeh” in Shia’ism.”
one of the mujhtahid-e-Fiqh has said this in his book Rozatul Janat Fi Ahwalil Ullama ‘o’ Saadaat by Allama Syed Mohd Baqar Moosvi Khwansari. Allama says and I qoute
“Mohd ibn -e- Junaid was a resident of Baghdad and was given a ‘Laqab’, QATIB. He is the first person who added the foundations of Ijtehad in Shi’ism and for Ehkam-e-Shariat he accepted the Sunni’s Usool-e-Fiqh. He lived in the same time as Mohammed bin Yaqoob-e-Kalni. Both of the above are called Two Qadeemi Fiqiyas by present day Fiqiyas, and the first person to accept the inclusion of Qayas ‘o’ Zan was Toosi .
The author further says that “Ibn Junaid has given many instructions against Yaqoob-e-Kalni – The author further confirms that Mohd bin Ahmed bin Junaid & Hassan bin Abi Aqueel Naumani were infact the first two persons to import Usool-e-Fiqh and the process of Ijtehad which is based on Qayas o Zan from Ahl-e-Sunnat sect of Islam.
Then came Shaikh Mufeed who favoured the idea of Zan & Qayas of Ibn-e-Junaid over the traditions of Imam which were quoted by Janab Yaqoob-e-Kalni. Sheikh Mufeed along with his followers spread the idea of Qayas & Zan and forwarded it to the next generation of Ullamas (The followers of Sheikh Mufeed included Shaikh Toosi and Syed Murtaza). It went on like this till Allama Hilli who made the rules which were brought in from Ahl-e-Sunnat as Compulsory and then Shaheed-e-Awwal and Shaheed -e-Saani adopted the very idea even strongly.