Shaami and other kutub mention the validity of the practice of kissing the fingers and rubbing on the eyes when the Muath-thin proclaims ‗Muhammadar R

Answer

The reason for labeling it Bid'ah, is on account of the corrupt belief of the Bid'atis. The Bid'atis have elevated this practice to the pedestal of Wujoob (compulsion). According to the Shariah if even a Mustahab act is elevated to the status of compulsion, it should then be abandoned. It will then enter into the domain of Bid'ah.