What is the ruling on saying "Always, eternally, everlastingly, there is no god but Allah" after the establishment of prayer, and is there a Sunnah supplication to be said afterwards?

This statement is good in itself, but the problem lies in its regular recitation after every iqama, because it has not been reported from the Prophet, peace and blessings be upon him. There is a fear that the regular recitation of this dhikr after every iqama might be an additive innovation (bid‘ah idafiyyah). What is prescribed after the iqama, according to many scholars, is to say what the mu'adhin says, then to send blessings upon the Prophet, peace and blessings be upon him, and to ask for the Wasilah for him.