Is the dinar and dirham a Sunnah of the Messenger (peace and blessings of Allah be upon him), and is abandoning them and using printed papers as money an innovation (bid'ah)?

There is nothing wrong with abandoning the use of dinars and dirhams, which were current during the time of the Prophet, peace and blessings be upon him. Nor is dealing in the banknotes known today considered an innovation (bid'ah), for innovations do not apply to customs. The dinars and dirhams in the time of the Prophet, peace and blessings be upon him, belonged to the Persians and Romans, and they did not bear the Quran or the name of Allah.