Hakeem bin Mu'awiyya bin Hayda حكيم بن معاوية بن حيدة القشيري · The Chapters on Business Transactions

'The Messenger of Allah (ﷺ) said: 'Dinar for Dinar, Dirham for Dirham, with no increase between them. Whoever has need of silver, let him trade gold for it, and whoever has need of gold, let him trade silver for it, and let the transaction be done on the spot."'