What is the ruling on an Imam who flirts with and pursues girls under the age of twelve and makes appointments with them inside or outside the mosque, and what is the ruling on one who knows of this and conceals it, and is it permissible to pray behind this Imam?

This action is impermissible, and its perpetrator must repent. If someone knows about it, they are obliged to advise and forbid him. If he responds, then that is well and good. Otherwise, it is obligatory to warn against him, expose him, and report his matter. Praying behind him depends on his response or lack thereof. If he repents, then there is no harm in praying behind him. But if he persists, then it is obligatory to remove him and appoint someone more righteous. If he cannot be removed, he is a transgressor (fasiq), and it is permissible to pray behind him, though it is better not to pray behind him and to seek out a just (imam).