Is it permissible to affix a supplication (du'a) to the wall of a bathroom that does not contain a toilet?

The authentic supplication after ablution is: "I bear witness that there is no god but Allah, alone, without partner, and that Muhammad is His servant and messenger." Whoever recites it will have the eight gates of Paradise opened for them. If the aforementioned supplication is not authentically narrated from the Prophet, peace be upon him, then it is not prescribed to consistently recite it after ablution, nor to display it inside the ablution area, as this might create the impression of its prescribed nature. However, if it is authentically narrated, there is no objection to displaying it, as long as it does not lead to its dishonor.