Is it permissible to pray in mosques where innovations (bidʻah) are widespread, or is it better to pray at home?

The command for congregational prayer is great, and its reward is immense. The abundance of steps towards mosques elevates ranks and expiates sins, and it is a sign of true faith. It is not permissible to abstain from it except for a legitimate excuse. Praying in a mosque free from innovations (bid'ah) and managed by those committed to the Sunnah is preferable, rather, it is obligatory if other mosques are managed by innovators. However, if a Muslim can only find mosques where innovations are prevalent, then he should consider the state of the Imam:

If the Imam is an innovator whose innovation constitutes disbelief (such as seeking aid from other than Allah or sacrificing to other than Him), then prayer behind him is not valid, and he must pray in his home.

If the Imam is an innovator whose innovation does not constitute disbelief, then prayer behind him is valid. He should go to the mosque and pray with them, and he should strive to advise the Imam and call him with wisdom and good admonition to abandon his innovation.