The Economic System of Islam by Taqiuddin an-Nabhani

When we talk about the silver standard (or the silver basis), what is meant is that silver forms the basis of the monetary unit, enjoys the freedom of coinage and is an unrestricted legal tender. This standard was well known in the past and was operating in the Islamic State alongside the gold standard. Some countries operated it as their main and only monetary standard. The silver standard continued to be operated in Indo-China until 1930 when the silver piaster was replaced with a golden one.

The silver standard is just like the gold standard in all its details. Therefore, operating the gold standard alongside the silver standard in the one State is a simple matter. The Islamic State operated the standards of gold and silver together since the Messenger of Allah (pbuh) emigrated to Madinah. This monetary policy should continue to be based on both the gold and the silver standard i.e. money should be in gold and silver, whether the circulation of this money is in real gold and silver or in banknotes backed by reserves of gold and silver wherever these notes are circulated.