Question 4: An Imaam of a Masjid (mosque) seeks help from dead people in their graves, claiming that these are the graves of Awliya’ (pious people) to whom we should resort. He says that they may act as mediators between us and Allaah (Exalted be He). Am I allowed to perform congregational Salaah (Prayer) behind this Imaam, despite the fact that I call for Tawheed (belief in the Oneness of Allaah)? Could you please also clarify such questions as making vows, seeking help from other than Allaah, and Tawassul (seeking to draw close to Allaah) through a means?
Answer: If you are sure that the Imam you mentioned seeks help from the dead or vows to them, then it is not permissible to perform Salah behind him because he is considered a Mushrik (one who associates others with Allah in His Divinity or worship); the Salah he performs… read more here.