From Sahih Muslim (Hadith 4075):
Fadala b. Ubaid al-Ansari reported:A necklace having gold and gems in it was brought to Allah's Messenger (ﷺ) in Khaibar and it was one of the spoils of war and was put to sale. Allah's Messenger (ﷺ) said: The gold used in it should be separated, and then Allah's Messenger (ﷺ) further said: (Sell) gold for gold with equal weight
Reference: Muslim 4075