A necklace having gold and gems in it was brought to Messenger of Allah ﷺ in Khaibar and it was one of the spoils of war and was put to sale. Messenger of Allah ﷺ said: The gold used in it should be separated, and then Messenger of Allah ﷺ further said: (Sell) gold for gold with equal weight.  

سَمِعْتُ فَضَالَةَ بْنَ عُبَيْدٍ الأَنْصَارِيَّ يَقُولُ أُتِيَ رَسُولُ اللَّهِ ﷺ وَهُوَ بِخَيْبَرَ بِقِلاَدَةٍ فِيهَا خَرَزٌ وَذَهَبٌ وَهِيَ مِنَ الْمَغَانِمِ تُبَاعُ فَأَمَرَ رَسُولُ اللَّهِ ﷺ بِالذَّهَبِ الَّذِي فِي الْقِلاَدَةِ فَنُزِعَ وَحْدَهُ ثُمَّ قَالَ لَهُمْ رَسُولُ اللَّهِ ﷺ الذَّهَبُ بِالذَّهَبِ وَزْنًا بِوَزْنٍ  

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.  

اشْتَرَيْتُ يَوْمَ خَيْبَرَ قِلاَدَةً بِاثْنَىْ عَشَرَ دِينَارًا فِيهَا ذَهَبٌ وَخَرَزٌ فَفَصَّلْتُهَا فَوَجَدْتُ فِيهَا أَكْثَرَ مِنِ اثْنَىْ عَشَرَ دِينَارًا فَذَكَرْتُ ذَلِكَ لِلنَّبِيِّ ﷺ فَقَالَ لاَ تُبَاعُ حَتَّى تُفَصَّلَ  

A hadith like this is narrated on the authority of Sa'id b. Yazid with the same chain of transmitters.  

عَنْ سَعِيدِ بْنِ يَزِيدَ بِهَذَا الإِسْنَادِ نَحْوَهُ  

We were in the company of Messenger of Allah ( 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 Messenger of Allah ﷺ said: Do not sell gold for gold but for equal weight  

كُنَّا مَعَ رَسُولِ اللَّهِ ﷺ يَوْمَ خَيْبَرَ نُبَايِعُ الْيَهُودَ الْوُقِيَّةَ الذَّهَبَ بِالدِّينَارَيْنِ وَالثَّلاَثَةِ فَقَالَ رَسُولُ اللَّهِ ﷺ لاَ تَبِيعُوا الذَّهَبَ بِالذَّهَبِ إِلاَّ وَزْنًا بِوَزْنٍ  

We were along with Fadala b. Ubaid (Allah be pleased with him) in an expedition. There fell to my and my friend's lot a necklace made of gold, silver and jewels. I decided to buy that. I asked Fadala b. 'Ubaid, whereupon he said: Separate its gold and place it in one pan (of the balance) and place your gold in the other pan, and do not receive but equal for equal, for I heard Messenger of Allah ﷺ as saying: He who believes in Allah and the Hereafter should not take but equal for equal.  

انْزِعْ ذَهَبَهَا فَاجْعَلْهُ فِي كِفَّةٍ وَاجْعَلْ ذَهَبَكَ فِي كِفَّةٍ ثُمَّ لاَ تَأْخُذَنَّ إِلاَّ مِثْلاً بِمِثْلٍ فَإِنِّي سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ كَانَ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ فَلاَ يَأْخُذَنَّ إِلاَّ مِثْلاً بِمِثْلٍ