Messenger of Allah ﷺ said, "Do not sell gold for gold unless equivalent in weight, and do not sell less amount for greater amount or vice versa; and do not sell silver for silver unless equivalent in weight, and do not sell less amount for greater amount or vice versa and do not sell gold or silver that is not present at the moment of exchange for gold or silver that is present. (Using translation from Bukhārī 2177)  

أَنَّ رَسُولَ اللهِ ﷺ قَالَ «لَا تَبِيعُوا الذَّهَبَ بِالذَّهَبِ إِلَّا مِثْلًا بِمِثْلٍ وَلَا تُشِفُّوا بَعْضَهَا عَلَى بَعْضٍ وَلَا تَبِيعُوا الْوَرِقَ بِالْوَرِقِ إِلَّا مِثْلًا بِمِثْلٍ وَلَا تُشِفُّوا بَعْضَهَا عَلَى بَعْضٍ وَلَا تَبِيعُوا مِنْهَا شَيْئًا غَائِبًا بِنَاجِزٍ»  

"My eyes saw and my ears heard the Messenger of Allah. And he mentioned the prohibition of (selling) gold for gold and silver for silver, unless it is equal amounts, like for like. And do not sell it in return for something to be paid later, and do not differentiate." (Using translation from Nasāʾī 4571)  

وَسَمِعَ أُذُنِي مِنْ رَسُولِ اللهِ ﷺ فَذَكَرَ النَّهْيَ عَنِ الذَّهَبِ بِالذَّهَبِ وَالْوَرِقِ بِالْوَرِقِ إِلَّا سَوَاءً بِسَوَاءٍ مِثْلًا بِمِثْلٍ وَلَا تَبِيعُوا غَائِبًا بِنَاجِزٍ وَلَا تُشِفُّوا أَحَدَهُمَا عَلَى الْآخَرِ  

Muawiyah sold a cup of gold or silver for more than its weight. Abu Ad-Darda' said: "I heard the Messenger of Allah forbid such transactions unless it was like for like." (Using translation from Nasāʾī 4572)  

أَنَّ مُعَاوِيَةَ بَاعَ سِقَايَةً مِنْ ذَهَبٍ أَوْ وَرِقٍ بِأَكْثَرَ مِنْ وَزْنِهَا فَقَالَ أَبُو الدَّرْدَاءِ سَمِعْتُ رَسُولَ اللهِ ﷺ يَنْهَى عَنْ مِثْلِ هَذَا إِلَّا مِثْلًا بِمِثْلٍ