What is the ruling on praying behind an imam of a mosque whose transgressions have been established by his own admission of flirting with women and listening to music, and his refusal to accept advice, given his father's inability to advise him?

If what has been reported about the immoral Imam is true, then he is in grave danger, and there is a fear for him of apostasy or a bad end, because he has taken the House of Allah as a place for his immorality and boasted of his disobedience. It is obligatory to offer him advice with wisdom and gentleness. If he responds, then that is good and blessed. If he persists, then a complaint must be submitted to the responsible authorities, or he should be prevented from leading the prayer if possible. If that is not possible, then prayer behind him should be abandoned as a form of disapproval, even though it is permissible to pray behind a wicked person if no other mosque is available. This Imam should know that his sin is not like the sin of others. A warning has been issued that the prayer of an Imam will not be accepted if those who pray behind him dislike him for his wickedness or innovation.