All praise is for Allah alone and may the Peace and Blesssings be on His messenger, and his family, and his companions.
a) The scholars of Usool (fundamentals) have mentioned definitions to clarify the true meaning and essence of taqleed, and from them is the saying of some of them that taqleed is the acceptance of a saying of a person without him knowing its evidence. And some of them [the scholars] held the view that taqleed is the acceptance of the saying of a person without argument. And Abu Ma'aali al-Juwayni chose the definition of taqleed that it is the following of one whose following is not based on proof and does not rely upon knowledge. And these definitions of the scholars of Usool, which are all close in meaning, have in it differences [in wording] which originate in the skill of enunciation, but the point here is to clarify the essence of taqleed in the manner of approximation.
b) And as for its categories along with the ruling of every category, then it is as follows:
1) Taqleed by the one who has the skills of ijtihaad, to others from the scholars after the truth has been made clear to him with confirmed evidences from the Prophet (s).
This is not permissable for him to do taqleed to what contradicts that which reached him from evidences and ijmaa’ (consensus).
2) Taqleed by the one who has been endowed the skill of ijtihaad, to one other than him from the mujtahideen before he reaches a ruling with his [own] ijtihaad.
Then it is not allowed for him to do taqleed to others.
[This is what] as-Shaafi'i, Ahmad, and others, Allah have mercy on them, held as their opinion, and is more correct, due to his ability to arrive at a ruling by himself. He is responsible for ijtihaad to know what the sharee’ah has made him liable for because of His saying, the Most High,
"So have taqwa of Allah as much as you are able,"
and what has been confirmed from the saying of the Prophet(s), "When I command you by a command, then follow it as much as you are able."
3) Taqleed of the one who is not able to research the evidences and derive rulings from it, to a scholar who has been endowed the skill of ijtihaad in the evidences of the sharee’ah.
This is permissible, due to His saying, the Most High,
"Allah does not burden a soul more than it can bear,"
and His saying, the Exalted,
"Then ask the people of remembrance [scholars] if you do not know,"
and other texts similar to these, which point to the removing of difficulty and the protection of the one responsible, from straying about in the rulings and speaking about Allah without knowledge.
4) The taqleed to the one who differs with the sharee’ah of Islam from the forefathers, leaders, and rulers, due to nationalism or following desires.
This is prohibited by ijmaa’. And verily many texts from the Qur'aan and Sunnah have been mentioned [in this]. And Allah, the Most High said, say:
'Rather we shall follow what we found our fathers following,' even though their fathers did not understand anything nor were they guided."[Baqarah:170]
And Allah, the Most High said,
"But no, by your Lord, they can not have faith until they make you judge in all disputes between them, and they find in themselves no resistance against your decisions, and accept with full submission."
And Allah, The Most High said,
"And it is not for a believer, man or woman, when Allah and His messenger have decreed a matter that they should have any option in their decision." [al-Ahzaab:36]
And the Most High said,
"And let those who oppose his [the Messenger's] commandment beware, lest some trials should befall on them or a painful torment be afflicted on them."[Noor:63]
And the Most High said,
"Say If you [indeed] love Allah, then follow me, Allah will love you and forgive you your sins."[Aali Imraan:31] And the Most High said,
"Verily Allah has cursed the disbelievers and prepared for them a flaming fire. They will abide in it forever, they will find no protector nor helper. On the day when their faces will be turned over in the Fire, they will say: 'Oh would that we had obeyed Allah and obeyed the Messenger. And they will say: 'Our Lord! Verily we obeyed our chiefs and our great ones, and they misled us from the right way. Our Lord! Give them double torment and curse them witht a mighty curse!" [al-Ahzaab:64-68]