Shaykh Ibn Taimiya, whom the non-followers consider as their Imam has ruled going against Taqleed Shakhsi as incorrect in his Fatawa. He writes:
As per their desires, people follow somebody who declares the Nikah as invalid and sometimes follow someone who declared Nikah as valid. This is not permissible.
He again writes in his Fatawa, Vol. 2, Pg. No. 24:
The person who cannot know the rules of the Shariah and follows a particular scholar, without knowing that there is another opinion more preferable than this, that person is to be praised. He will be rewarded. Neither will he be condemned, nor will he punished.
His famous student Ibn Qayyim Al Jawzi, writes in A’alaam Ul Mauqae’een:
Unless the qualifications of Ijtihad (legislation) are not seen in a person, it is not permissible for him to extract rules from the Holy Quran and the Hadith.
These lines establish the compulsory nature of Taqleed. Now, the question is that there have been many Legislators (Mujtahidin), so, why follow the 4 Imams only?
The detailed manner in which the rules extracted by the 4 Imams are available to us, chapter wise, right from Kitab Ut Taharah to Kitab Ul Faraaidh and in extreme detail. The rules extracted by the other Imams are not available in the same manner. The universal acceptance of these 4 Imams has not been given to others. That’s why these 4 Imams are followed.
Except the 4 Imams, all other true schools of Jurisprudence have ceased to exist. For this reason, it is the consensus of the whole Ummah that to follow any of the 4 Imams is to follow the Sawaad-e-A’adham i.e. to follow the Ahle Sunnah. To abandon them is to abandon the Sawaad-e-A’adham, as Hadhrat Shah Waliullah (May Allah shower His mercy on him) as written in Uqd Al Jayyid Fil Ahkaam Il Ijtihad Wa Taqleed.
Allama Ibn Nujaim Misri (May Allah shower His mercy on him) has written in Al Ashba Wan Nadhaair:
Translation: Those who turn away from the 4 Imams are against the consensus of the Ummah.
These are a few lines about the nature of Taqlid and clarifications about it. Taqlid is the consensus of the Ummah and those who go against are going against the consensus of the whole Ummah. For this reason, all the great scholars and saints have been followers of any one of these 4 Imams. This is the path of truth and the path of guidance.