What is the ruling on praying behind an Imam who takes usurious loans in the names of his children?

Consuming usury and borrowing with it are grave sins. The Imam who deals in usury must be advised and reminded of the gravity of his actions, supported by verses and Hadiths warning against usury. As for praying behind him, it is valid according to the preponderant opinion, despite the dislike of praying behind a fasiq (transgressor). Praying behind others who are just is more preferable.