What is the ruling on praying behind an imam who treats himself with sorcery?

The validity of prayer behind an imam who practices sorcery cannot be determined without knowing the reality of his actions. If the sorcery involves acts of shirk (associating partners with Allah), then prayer behind him is impermissible, and he must be removed from the imamate. However, if it does not amount to shirk, or if he does not believe in it, then it is preferable to avoid praying behind him, but the prayer is valid unless shirk is definitively established.