Is it permissible to pray behind people of innovation, such as the Sufis?

Do not pray behind an innovator (mubtadi') unless you find no one else, and it is obligatory upon you to advise him and clarify the truth to him. If his innovation is one that leads to disbelief (mukaffirah), such as seeking help from other than Allah, or slandering the Companions, or believing in the incompleteness of the Qur'an, then prayer behind him is not valid. However, if his innovation does not lead to disbelief, then prayer behind him is valid.