Is it permissible to pray behind an imam who commits bidʻah (innovation in religious matters) and holds polytheistic beliefs?

Innovation (bid'ah) is either one that constitutes disbelief (kufr), such as the innovation of the Jahmiyyah, the Rawafidh (Shiites), and the doctrines of hulul (incarnation) and ittihad (union with God). Prayer behind such individuals is not valid. Or, the innovation is one that does not constitute disbelief, such as verbalizing the intention (nawiyyah) or gathering for dhikr (remembrance of God) in the manner practiced by Sufis. Prayer behind these individuals is valid, but they should be advised to abandon these innovations. It is preferable to seek an imam who is keen on following the Sunnah.

Shaykh al-Islam Ibn Taymiyyah mentioned that the innovation by which a man is considered among the people of desires (ahl al-ahwa') is that which is well-known among the scholars of Sunnah for contradicting the Qur'an and Sunnah, such as the innovation of the Khawarij, the Rawafidh, the Qadariyyah, and the Murji'ah. The Jahmiyyah are not part of the ummah of Muhammad (peace be upon him), and they deny the divine attributes. As for the Rawafidh in these times, in addition to their rejectionism, they are Jahmiyyah and Qadariyyah, and they may even adopt the doctrines of the Isma'iliyyah and similar groups.

Furthermore, the scholars of the Permanent Committee (for Islamic Research and Fatawa) clarified that if the innovation of the innovator is shirk (polytheism), such as supplicating to other than Allah, then prayer behind them is not valid. However, if their innovation is not shirk, such as dhikr performed in gatherings with swaying movements, then prayer behind them is valid. Nevertheless, it is preferable to seek a non-innovating imam to gain more reward and to avoid evil.