What is the ruling on calling to tawhid (the oneness of Allah) in a mosque that mixes the Sunnah with other schools of thought, such as the Sufis and the Asha'irah?

Question:
This is a questioner from Britain who says: We have some mosques in Britain where they bring a man on the methodology of the Sunnah to teach people tawhid (the oneness of Allah) or give them a lecture on tawhid. Then the next day they bring a Sufi or an Ash'ari to teach people Sufism or Ash'arism. The question is: Is it permissible for this Sunni caller to teach in such mosques?

Answer:
No, if they mix it with what is bid'ah (religious innovation) and deviant, it is not permissible for him to do so, because they use him as a cover. They use him as a cover and say, "We teach tawhid, and we allow lectures on tawhid." This is not allowed. This is mixing truth with falsehood. He should set a condition with them, saying, "I will teach you, or I will be present with you, but on the condition that you do not bring someone who contradicts what I am calling you to and telling you." Yes.