Sahih Muslim
The Book of Transactions (Kitab Al-Buyu)
Book Number: 010 / Hadith Number: 3863
Fadala b. Ubaid al-Ansari reported: A necklace having gold and gems in it was brought to Allah's Messenger (may peace be upon him) in Khaibar and it was one of the spoils of war and was put to sale. Allah's Messenger (may peace be upon him) said: The gold used in it should be separated, and then Allah's Messenger (may peace be upon him) further said: (Sell) gold for gold with equal weight.