Is prayer valid behind an Imam who does not attend Fajr and Isha prayers in the mosque, even though he mentions their virtue, or behind another Imam who enjoins good and forbids evil, yet does the opposite himself?

A Muslim must align their words with their actions, especially one who undertakes to lead the prayers (Imam), deliver sermons (Khutbah), and admonish people, and they must avoid major sins. If the Imam lags behind in congregational prayers without a valid Shar'i excuse or commits forbidden acts, the mosque community should advise him, warn him of Allah, and strive to establish a just Imam. Scholars have differed regarding the validity of prayer behind a transgressor (Fasiq), and we advise against abandoning prayer in the congregational mosque until a righteous Imam is established. As for an Imam who openly supports polytheists against Muslims, he has committed one of the nullifiers of Islam, and prayer behind him is not valid.