Ruling on praying behind an evildoer
Question

                What is the ruling on praying behind an imam who was sodomized during his childhood and youth with his consent, knowing that he has a beautiful voice and has memorized the entire Qur’aan?.
Praise be to Allah.
      Firstly: 
If this imam has repented 
    and changed his ways for the better, then there is nothing wrong with 
    appointing him as an imam to lead others in prayer, or with praying behind 
    him. No one has the right to criticize him or punish him for a sin from 
    which he has repented. Allaah says (interpretation of the meaning): 

    “verily, Allaah forgives all sins”

    [al-Zumar 39:53]

    i.e., for the one who repents. 

    The Prophet  (peace and blessings of Allaah be upon him) 
    said: “The one who repents from sin is like one who did not sin at all.” 
    Narrated by Ibn Maajah, 4250; classed as hasan by al-Albaani in Saheeh 
    Ibn Maajah. 

    But if he is still committing that great evil, he must be 
    advised and warned and made to fear Allaah. If he does not repent, then 
    efforts must be made to prevent him from leading the prayer and he should be 
    replaced with another, righteous imam who adheres properly to his religion 
    and is keen to attain the quality of taqwa. The Prophet  (peace and 
    blessings of Allaah be upon him) forbade a man to spit in the direction of 
    the qiblah whilst praying, and he forbade him to lead his people in prayer, 
    and he said to him: “You have offended Allaah and His Messenger.” Narrated 
    by Abu Dawood, 481 and classed as hasan by Shaykh al-Albaan in Saheeh 
    Sunan Abi Dawood. So how about one who commits this great evil? He is 
    more deserving of being prevented from leading the prayers! 

    Moreover, appointing him to lead the prayers is a form of 
    showing respect to him, and an evildoer is not deserving of such respect. 

    The imam is usually someone whom the people take as an 
    example and from whom they learn and receive guidance. The more just and 
    righteous he is, the more that will benefit the people and make them more 
    likely to accept what he says. 

    But if he is an evildoer, the people will not accept anything 
    from him, rather he may be the cause of some of them being led astray, 
    Allaah forbid. 

    Secondly: 
With regard to the 
    validity of prayers offered behind an evildoer, the imams (scholars) 
    differed concerning that. The view of the majority is that a prayer offered 
    behind such a person is valid, although it is makrooh. 

    Al-Nawawi said in al-Majmoo’, 4/151: 

    It is proven in Saheeh al-Bukhaari that Ibn ‘Umar 
    prayed behind al-Hajjaaj ibn Yoosuf, and many other saheeh ahaadeeth 
    indicate that prayers offered behind evildoers and unjust rulers are valid. 

    Our companions said: Prayers offered behind evildoers are not 
    haraam, but they are makrooh. It is also makrooh to pray behind an innovator 
    whose bid’ah does not reach the degree of kufr, but such prayers are valid. 
    But if his bid’ah constitutes kufr then as we have stated before, prayers 
    offered behind him are not valid as is the case with any other kaafir. 
    Al-Shaafa’i stated in al-Mukhtasar that it is makrooh to pray behind 
    an evildoer or an innovator, but if one does that, the prayer is valid. 

    End quote 

    Shaykh al-Islam [Ibn Taymiyah] said in Majmoo’ al-Fataawa, 
    23/341: 

    If there are two men of religious commitment, then whichever 
    of them has more knowledge of Qur’aan and Sunnah should be given precedence… 
    If one of them is an evildoer, such as if he is known for lying or being 
    treacherous and so on, and the other is a believer and is pious, then the 
    latter is more entitled to lead the prayers if he is qualified to do so, but 
    if the former has more knowledge of Qur’aan and is more knowledgeable, then 
    prayer behind the evildoer is emphatically forbidden according to some 
    scholars and is disliked according to others… and it is not permissible to 
    appoint the evildoer when it is possible to appoint the righteous man. 

    He also said (23/375): 

    It is not permissible to appoint someone to lead the prayers 
    who consumes hashish or does evil and haraam things when it is possible to 
    appoint someone who is better than him. 
The imams are agreed that 
    it is makrooh to pray behind an evildoer, but they differed as to whether 
    such a prayer is valid. It was said that it is not valid, as is the view of 
    Maalik and Ahmad according to one of the two reports narrated from them. And 
    it was said that it is valid, as is the view of Abu Haneefah and 
    al-Shaafa’i, and the other view narrated from Maalik and Ahmad. But there is 
    no dispute concerning the fact that such a person should not be appointed. 
    End quote. 

    See also al-Sharh al-Mumti’, 4/403-308 

    Thirdly: 

    The scholars have discussed in detail what should be done 
    with an evildoer imam. It says in Fataawa al-Lajnah al-Daa’imah: 
Based on this, if he is 
    the imam of a mosque and he does not pay heed to advice, then he must be 
    removed if possible and if that will not lead to fitnah (tribulation), 
    otherwise those who are able to should pray behind someone else who is 
    righteous, as a rebuke to him and a denunciation, so long as that will not 
    lead to fitnah (tribulation). 

    If it is not possible to pray behind someone else, then it is 
    prescribed to pray behind him, so as to preserve the interests of the 
    jamaa’ah (group or congregation). 

    If there is the fear that praying behind someone else will 
    provoke fitnah, then (the people) should pray behind him so as to ward off 
    fitnah and so as to do the lesser of two evils. 

    From Fataawa al-Lajnah al-Daa’imah, 7/370 

    And Allaah knows best.