What is the ruling on an Imam who falsely testified that the husband did not beat his wife, nor spend on her, nor abandon her, while it was the wife who abandoned the husband? Is it permissible to pray behind him, and is it obligatory to expose him?

If it is established that the Imam bore false witness, he has committed a grave sin, unless he was observing a legitimate religious interest that could not be achieved except through lying. However, that does not prevent praying behind him if his prayer is valid. It is preferable to pray behind an upright person. It is not permissible to expose him, because the Lawgiver commanded the concealment of believers. However, it is permissible for someone who is certain of the contrary to his testimony to testify truthfully before the judge.