Is it permissible to pray in the mosques of the Sufis, and does the ruling differ according to the nature of their Sufism?

Question:
Honorable Shaykh, may Allah grant you success, a questioner from outside this country says: The mosque in our village is a mosque for the Sufis. So, should I come and pray the congregational prayer with them in this mosque?

Answer:
If you find another mosque that is better, go to it. If you do not find one, then look into these Sufis: if their Sufism leads to disbelief, do not pray with them. If their Sufism is merely a religious innovation (bid'ah), pray the congregation with them. The ruling differs between what is disbelief and what is not.