Buying and Selling: Handing Over Gold and Silver Before Departing
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 2131
If gold or silver is sold for gold or silver, the seller and buyer must hand over the commodity and the payment in exchange to each other before they depart from each other. If they do not hand over any amount of the thing that they had agreed on, the transaction is invalid. If they hand over part of it, the transaction relating to that part is valid.
-Ayatullah Sistani, Practical Laws of Islam, Buying and Selling