Prayer: Realising the Imam's Ineligibility or Invalid Prayer After Prayers
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1401
If after prayers a follower realises that the imam was not a dutiful person, or that he was a disbeliever, or for some reason his prayer was invalid – for example, he performed it without wuḍūʾ – his prayer is valid.