What is the ruling on praying behind imams in Bangladesh who perform Bid'ah (innovations in religion), such as seeking intercession (Tawassul) and celebrating the Prophet's birthday (Mawlid)? And what is the method for advising them and clarifying the truth to them?

There is a detailed explanation regarding praying behind an innovator (Mubtadi'): If no other Imam is available, such as for Friday prayers, Eid prayers, or Hajj, then praying behind him is permissible by the consensus of the Ahl al-Sunnah wal-Jama'ah, especially if the innovation is not an act of disbelief (kufr). However, if his innovation is polytheistic (shirk) and an act of disbelief, then prayer behind him is not valid. If it is possible to pray behind someone who is not an innovator, that is preferable. The innovator should be advised and called to the truth with evidence and proof.