What is the ruling on a Tijani Zawiya Imam and some of his followers performing strange movements and spreading a long white cloth after Asr prayer, especially on Friday? Are these actions considered Bid'ah (innovation), and is praying behind this Imam valid?

The Tijaniyya tariqa is an innovation. They believe in the possibility of meeting the Prophet, peace and blessings be upon him, physically in this world. They also claim that the Prophet specifically granted them the prayer "Fatih Lima Ughliq" (Opener of What is Closed). The Tijanis innovate in their acts of worship by dedicating supplications not found in Islamic law and by obligating people to specific acts of worship at specific times. Furthermore, they hold beliefs that lead one out of the fold of Islam, such as their belief in hulul (incarnation) and ittihad (union with God). Praying behind them is not permissible if there is an option to pray behind others. However, if it is impossible to do otherwise, then there is no harm in praying behind them, except for those who are known to believe in hulul and ittihad or other disbelieving innovations, in which case praying behind them is never permissible.