Rulings on ijtihaad in Islam and the conditions to be met by the mujtahid
Question

                What is the ruling on ijtihaad in Islam? What are the conditions to be met by the mujtahid?.
Praise be to Allah.
    Ijtihaad in Islam means striving to understand the shar’i 
    ruling on the basis of shar’i evidence. It is obligatory for the one who is 
    able to do it, because Allaah, may He be glorified and exalted, says 
    (interpretation of the meaning): 

    “So ask of those who know the Scripture, if you know not”

    [al-Nahl 16:43, al-Anbiya’ 21:7].

    The one who is able to engage in ijtihaad can find out the 
    truth for himself, but he must have vast knowledge and study the shar’i 
    texts, and understand the guidelines on deriving rulings and be aware of the 
    views of the scholars, lest he fall into that which is contrary to Islam. 
    Some people are seekers of knowledge (taalib al-‘ilm) who have only a little 
    knowledge, but they set themselves up as mujtahids, so you see them acting 
    on the basis of ahaadeeth which are general in meaning but have other 
    reports which make them specific, or they act on the basis of abrogated 
    ahaadeeth and do not know of the texts that abrogate them, or they act on 
    the basis of ahaadeeth which the scholars are unanimously agreed are 
    different from their apparent meanings, but they are unaware of this 
    scholarly consensus. 

    Such a person is in grave danger. The Mujtahid must have 
    knowledge of the shar’i evidence and knowledge of the basic principles 
    (usool) and scholarly views which, if he knows them, he will be able to 
    derive rulings based on that evidence without unwittingly going against 
    scholarly consensus. If these conditions are met in his case, then he may 
    engage in ijtihaad. Ijtihaad may be focused on a narrow area, so a person 
    may research one issue of knowledge and examine it thoroughly, and become a 
    mujtahid with regard to that issue, or he could focus on one aspect of 
    knowledge, such as issues having to do with tahaarah (purification), which 
    he researches and examines, and thus becomes a mujtahid in that area. End 
    quote. 

    Fatwa of Shaykh Ibn ‘Uthaymeen, signed by him.