Praying behind an imam who commits some sins
Question

                We have an Imam here in the mosque ... he shaves his beard partly ... that is, he is not completely clean shaven but he keeps a thin beard on his face and he is a hafiz ... the problem is that there are many people praying behind him who seem to b better to him in following the religion , even though they r not hafiz of the Qur'an ... question is does his bidah of keeping a thin beard only, invalidate his prayers, and as a consequence, the prayers of those praying behind him .... and secondly, even his prays r valid, should we strive to replace him with sumone who is better in following the religion, for example, sumone who does not shave or trim his beard , even if he is not a hafiz ... 

please answer in detail with evidence from the Qur'an and Sunnah and please answer soon ... we r having a lot of problems in our mosque because of this issue ...some say that we must not pray behind him while others say that we must pray behind him.
Praise be to Allah.
    Firstly: 
Shaving the beard in 
    whole or in part is a sin which is not permissible to do. The prayer of one 
    who commits a sin such as shaving the beard and the like is valid if he does 
    it as prescribed by Allaah, according to scholarly consensus. The prayers of 
    those who pray behind him, if he leads the prayer, are also valid, according 
    to the more correct of the two scholarly opinions. 

    Tuhfat al-Ikhwaan, p. 114, by 
    Shaykh ‘Abd al-‘Azeez ibn Baaz. 

    The fact that his leading of the prayer is valid is indicated 
    by the fact that the Sahaabah (may Allaah be pleased with them) prayed 
    behind unjust leaders and ruler. ‘Abd-Allaah ibn ‘Umar and Anas (may Allaah 
    be pleased with him) prayed behind al-Hajjaaj al-Thaqafi. Al-Shaafa’i said: 
    And he – meaning al-Hajjaaj – was bad enough (as an evildoer).  

    Once this is established, there is no point in saying, “I 
    will not pray behind this imam.” Rather you should pray behind him if not 
    doing so will lead to evil consequences, division or conflict, because 
    conflict is worse. 

    Shaykh Ibn Baaz (may Allaah have mercy on him) said: If by 
    not praying behind him the worshipper will miss out on Jumu’ah and prayers 
    in congregation, then no one does that except an innovator who is differing 
    from the Sahaabah (may Allaah be pleased with them). Similarly, if the imam 
    has been appointed by those in authority and there is no shar’i purpose to 
    be served by not praying behind him, then you should not refuse to pray 
    behind him, rather it is better to pray behind him. 

    Majmoo’ Fataawa al-Shaykh Ibn Baaz, 
    9/388. 
Al-Nawawi (may 
    Allaah have mercy on him) said – concerning one who leads people in prayer 
    when they do not like him: Our companions said: His leading the prayer is 
    makrooh if they dislike him because of something that is condemned in 
    sharee’ah, such as an oppressive ruler or one who attains the position of 
    imam by force and does not deserve it, or one who does not take precautions 
    to avoid naajis (impure) things… If no such thing applies then it is not 
    makrooh. … Then he said: When we say that it is makrooh, that is limited to 
    the imam; as for the members of the congregation who do not like him, it is 
    not makrooh for them to pray behind him. 

    Al-Majmoo’, 4/172-173 

    Secondly: 
With regard to replacing 
    him, if you are able to replace him with another imam who is more 
    religiously committed and doing so will not result in a greater evil, then 
    it is better to do that, otherwise it is better to leave him. 

    The evidence that an imam who commits sin openly should not 
    be allowed to lead the prayers is to be found in the report narrated by Abu 
    Dawood (481), which says that a man led some people in prayer and he spat in 
    the qiblah (of the mosque) when the Messenger of Allaah  (peace and 
    blessings of Allaah be upon him) was looking on. The Messenger of Allaah 
     (peace and blessings of Allaah be upon him) said, when he had finished 
    praying: “He should not lead you in prayer.” After that he wanted to lead 
    them in prayer again, but they did not let him, and they told him what the 
    Messenger of Allaah  (peace and blessings of Allaah be upon him) had 
    said. He mentioned that to the Messenger of Allaah  (peace and blessings 
    of Allaah be upon him) and he said: “Yes.” And I (the narrator) think that 
    he said: “You have offended Allaah and His Messenger.” Classed as hasan by 
    al-Albaani in Saheeh Abi Dawood. 
This is so long as 
    preventing him from leading the prayers will not lead to a greater evil; if 
    that is the case, then you should pray behind him, and it is not permissible 
    to refrain from praying in congregation because of the evildoing of the 
    imam, as stated above. 

    Shaykh Ibn Baaz (may Allaah have mercy on him) said: If it is 
    possible for a person to prevent a person who commits evil openly from 
    leading the prayer, then he has to do that; but if he has been appointed by 
    someone else and it is not possible to stop him leading the prayers or it is 
    only possible to stop him by means of a greater evil that is more harmful 
    than the evil of the imam who commits evil openly, then it is not 
    permissible to ward off a lesser evil by means of a greater one. Islam came 
    to achieve and complete what is in people’s best interests and to wipe out 
    and reduce evil as much as possible. 

    Majmoo’ Fataawa al-Shaykh Ibn Baaz, 
    9/377 

    See also question no. 
    13465 

    And Allaah knows best.