Is it permissible to pray behind an imam who is one of the people of innovation, upon whom some differences in ablution are apparent, such as wiping over the tops of the feet, while his outward prayer is like ours?

Ablution is not valid by wiping the feet, and consequently, prayer performed with such ablution is invalid, as is praying behind someone who does so, except for one who is ignorant of his condition. Similarly, prayer behind someone who holds disbelieving beliefs is not valid.