An Outline of the History of Restriction on Ijtihad
Similarly, many eminent scholars who have lived throughout these centuries down to our own times did not submit to the restriction on the madhahib and did not believe that any Islamic precept made it obligatory upon all Muslims to follow one of the four Imams or made it unlawful for them to go beyond their rulings in matters of ahkam, which cannot be known except through inference from the Qur'an and the Sunnah. That is because none of the sources of Islamic law, i.e. the Qur'an, the Sunnah, consensus (ijma') and reason ('aql), proves this restriction.
Adherence to any madhhab was not known to the Muslims from the time of advent of Islam up to the period when the four madhahib gained currency, and this was nearly after two centuries. But even then, though the concept of madhhab had developed among them, the restriction making it obligatory to follow one of the four madhahib and proscribing others, as mentioned earlier, took place in the 7th/13th century at the caliph's orders for political reasons. Otherwise, the ability to deduce the ahkam from the Qur'an and the Sunnah is neither confined to any particular country, nor limited to particular persons to the exclusion of others.
Abu al-Tayyib Siddiq Hasan Khan, in Husal al-ma'mul min 'ilm al-usul, p. 186, while rejecting the limitation on madhaab to the four and calling for the revival of ijtihad, observes:
One who limits the grace of God to some of His creatures and confines the ability to understand the sacred Shari'ah to those of the past eras, is guilty of insolence towards God Almighty and His Shari'ah, which has been laid down for all His servants who adhere to the Qur'an and the Sunnah. If adherence to the Holy Quran and the Sunnah is limited to the people of the bygone ages and if there remains nothing for those who came after them to do except imitate their predecessors, and if they cannot deduce the knowledge of God's laws from the Qur'an and the Messenger's sunnah, what are the grounds of this false distinction and this spurious dogma? Is naskh (abrogation) anything other than this? Glory be to God, this is a great calumny! 
Muhammad Farid Wajdi, a contemporary writer, in the third volume of the Da'irat al-ma'arif, at the beginning of his discussion on ijtihad, under the root j-h-d, says:
When the Muslims were afflicted by the malaise of social stagnation and affected by the inability to understand the secrets of the Shari'ah, they took resort in the excuse of the closure of the gates of ijtihad and legal inference to conceal their own weakness. The truth is that this door remains open, as affirmed by express statements of the Qur'an and the Sunnah, till the Day of Resurrection. 
Then, in nearly sixty pages, he presents his research about ijtihad, the details of its various phases, its history, and its perpetual necessity.
In short, to consider ijtihad as permissible for the early generations and unlawful for the later generations is a form of baseless discrimination, acceptable to none except those whom Abu al-Tayyib al Siddiq Hasan Khan calls `captives of taqlid'. He says: "The captives of taqlid are not like those to whom God has opened the doors of the higher teachings (ma'arif) and given them a knowledge with which they free themselves from the imitation of men." 
There are other scholars of repute among later as well as the contemporary generations, among them Shaykh Muhammad `Abduh and his pupil, the author of al-Manar, as well as other outstanding and independent contemporary thinkers who have freed themselves from the yoke of taqlid and declared their opposition to those who consider the door of ijtihad as closed.
[Partisans of Restriction on Ijtihad:]