The ruling on designating a specific day for fasting and supplication

Question:
He says: Sometimes phrases are posted in some mosques saying, “Limit your supplication to this day for such and such,” or “Fast on the Thursday corresponding to such and such, then make supplication.” Sometimes the imam invites his congregation to do this. What is the ruling on such a thing?

Answer:
This is a bid'ah (religious innovation). It is telling people to fast on a specific day for which there is no evidence designating it, or to recite a supplication for which there is no evidence designating it. This is a bid'ah, and one must deter people from this action. If it is known and recognized, one must deter people from this action, because innovations arise from such things little by little. It is not permissible for a person to hold back something from his own mind.
Even if the original act is prescribed, restricting it to a time, place, or number for which there is no evidence makes it a bid'ah. This is called an additional bid'ah. An additional bid'ah is when the original act is prescribed, but something not prescribed is added to it.