Is it permissible to pray behind an imam who prolongs the khutbah, insults people, and praises himself, or is it better to go to another mosque, or pray at home or at work due to the absence of a third mosque?

What the Imam does, by insulting people, is a reprehensible act. It has been authentically reported that the Prophet, peace and blessings be upon him, said: "Insulting a Muslim is a perversion (fusooq), and fighting him is disbelief (kufr)." His claim that he is the most knowledgeable person in the mosque is inappropriate, for knowledge is about awe of Allah (khashyah) and not about extensive narration. Prolonging his sermon is contrary to the Sunnah, as the Prophet, peace and blessings be upon him, said: "Indeed, the length of a man's prayer and the brevity of his sermon are indications of his understanding (fiqh)."

Therefore, he should be advised gently and kindly, and his error should be clarified to him. It is permissible to pray in another mosque whose Imam leads the prayer well, or to pray at home or at work in congregation for prayers other than Jumu'ah (Friday prayer). As for Jumu'ah, it must be attended in the mosque.

An Imam who leads people in prayer when they dislike him for a legitimate Shar'i (Islamic legal) reason may expose himself to sin, and his prayer might be invalid. Some scholars have even considered this forbidden if the dislike is due to a religious reason, and if those who dislike him constitute the majority of the congregants. So, he must hasten to rectify his errors.