Fadalah bin Ubaid · The Book of Musaqah

I bought on the day (of the Victory of Khaibar) a necklace for twelve dinars (gold coins). It was made of gold studded with gems. I separated (gold from gems) in it, and found (gold) of more (worth) than twelve dinars. I made a mention of it to Allah's Apostle (ﷺ), whereupon he said: It should not be sold unless it is separated.

We were in the company of Allah's Messenger ( may peace be upon him) on the day (of the Victory of) Khaibar, and made transaction with the Jews for the 'uqiya of gold for the dinars or three (gold coins), whereupon Allah's Messenger (ﷺ) said: Do not sell gold for gold but for equal weight