Narrated Fudalah bin Ubaid: We were with the Messenger of Allah ﷺ at the battle of Khaibar. We were selling to the Jews one uqiyah of gold for one dinar. The narrators other than Qutaibah said: "for two or three dinars. " Then both the versions agreed. The Messenger of Allah ﷺ said: Do not sell gold except with equal weight.
Hadith Referenceسنن ابي داود / كتاب البيوع / 3353
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم (1591)
Hadith Takhrij« انظر حدیث رقم (3351)، (تحفة الأشراف: 11027) (صحیح) »
Benefits and Issues: ➊ When gold is exchanged for gold, or silver for silver, it is necessary that the weight be equal and the transaction be immediate (hand to hand). ➋ Otherwise, it will constitute usury (riba). ➌ In the case where gold is mixed with another substance, it should be separated. ➍ In mixed items, the correct weight of gold or silver cannot be determined until they are separated. ➎ After separating, the price of everything attached to the gold or silver will also be determined separately, and there will no longer be any possibility of usury (riba).
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 3353