What is the ruling on dealing with banknotes through buying and selling currencies with the intention of trading or fulfilling a need in a foreign country?

It is permissible to buy currencies for trading or other needs, provided that their sale adheres to the Shariah rulings for currency exchange. A single currency is considered one type, in which no surplus (riba) is allowed (it is not permissible to sell one hundred units of it for one hundred and ten). Paper currencies take the place of gold and silver in terms of their monetary value, and the same rules that apply to the two precious metals (gold and silver) apply to them. When selling one currency for another (e.g., dinars for dollars), immediate possession (al-taqabud) in the contract session is required, and deferment (al-nasi'ah) is not allowed. While surplus (riba) is forbidden within the same currency type, it is permissible between two different types of currencies if exchanged hand-to-hand.