Is it permissible to pray behind an imam who has usurped a house or a piece of land?

Scholars differed regarding the validity of prayer behind a transgressor (fasiq). The most preponderant opinion is that prayer behind him is valid, though disliked, provided his own prayer is valid. Imam Al-Shafi'i held that prayer behind a transgressor is sufficient and does not require repetition. Some Malikis are of the view that if the Imam's transgression is unrelated to the prayer, such as usurpation or adultery, it does not affect the validity of his imamate.