An Outline of the History of Restriction on Ijtihad
. Al-Maqrizi, al-Khutat (al-Mawa'iz wa al-i'tibar bi dhikr al-khulal wa al athar), ii, 332
. Refer to al-Ghadir the encyclopaedic work of 'Allamah Amini (quddisa sirruh), wherein one can find numerous sources which prove this point.
. Al-Ya'qubi, Ta'rikh (Najaf), ii, 102.
. This is a mutawatir tradition of the Prophet (s) narrated both by Sunnis and Shi'is. See, for instance: Ta'rikh Baghdad, ii, 337; Kifayat al-talib, bab 58, p. 220, Tadhkirat al-khawass, "hadith madinat al-ilm," p. 47; Dhakha'ir al-'uqba, p. 77; Usud al-ghabah, the biographical account of 'Ali ('a), iv, p. 22; Tahdhib al tahdhib, the biographical account of 'Abd al-Salam (Abu al-Salt al-Harawi), vi, 320.
. This is a mutawatir tradition accepted by both the Sunnis and the Shi'ah, and has been transmitted by more than 200 scholars from more than thirty Companions, men and women. See, for instance: Sahih Muslim, iv, "fadail 'Ali ('a)," traditions 36 and 37; Sunan al-Tirmidhi, v, bab 32; al-Darimi, Sunan, ii, "fada'il al Qur'an"; al-Nisa'i, al-Khasa'is (Najaf), p. 93; Kifayat al-talib (Najaf), p. 50; Dhakha'ir al-'uqba, "bab al-fadl Ahl al-Bayt," p. 16; Tadhkirat al-khawass (Najaf), bab 12, p. 322; Yanabi' al-mawaddah, p. 30; Usud al-ghabah, ii, the biographical account of al-Hasan ibn 'Ali ('a), p. 12; al-Ya'qubi, Ta'rtkh (Najaf), ii, 102; al-Hakim al Nayshaburi, al-Mustadrak 'ala al-Sahihayn, "kitab ma'rifat al-Sahabah," "fadail 'Ali ('a)," iii, 109; Musnad Ahmad, iii, 17, the traditions of Abu Sa'id al-Khudri; v, 371, the traditions of Zayd ibn Arqam; and v,181, the traditions of Zayd ibn Thabit.
Also refer to Risalat Hadith al-Thaqalayn by al-Shaykh Qiwam al-Din al-Qummi al-Wishnawi (Dfir al-Taqrib li al-Madhahib, Egypt). For further details on this issue, see the first two volumes of 'Abaqdt al-anwar.
(The reader may also profitably refer to the long article "Hadith al-Thaqalayn: a Study of its Tawatur", published in five parts in al-Tawhid, vol. viii, nos.1-4, vol. x, no. 4. -Translator)
. Al-Tehrani, al-Dharrah, i, 13. Refer to the details mentioned in ii, 134 on the discussion about the usul works under the root a-s-l. There one finds the definition of 'asl,' the difference between an asl and a kitab, and the number of the usul, the names of their writers and the ones that are extant.
For a better appreciation of this issue refer to Diya' al-dirayah of al-Sayyid Qiya' al-Din al-Allamah, p. 70, and the first issue of the series Ihya' Turath Ahl al-Bayt under the title Dirasah hawl al-usul al-arba'ah mi'ah, by al-Sayyid Muhammad Husayn al Husayni al-Jalali, also printed in Da'irat al-maarif al-Shi'iyyah (Beirut), vol. 5.
. Obviously ijtihad is not limited to this; rather it is only a part of ijtihad.