It was narrated from Umar bin Muhammad bin 'Ali bin abi Talib, from his father, that his grandfather said:
'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."'