Is it permissible to tell someone: "What you are doing is Haram (forbidden) or Bid'ah (innovation)," based on a fatwa you saw, without ensuring there is a consensus on the matter?

Whoever is asked about a Sharia ruling he does not know can convey the fatwa and its source to the questioner, while guiding him to ask trustworthy scholars. He is not obliged to clarify if he is not certain that the act is reprehensible. Denouncing it and asserting it to be reprehensible in this situation is not permissible.