"O people, you have invented kinds of transactions, I do not know what they are, but make sure it is gold for gold, of the same weight, or silver for silver, of the same weight. There is nothing wrong with selling silver for gold, hand to hand, giving more silver than gold, but no credit is allowed. When you sell wheat for wheat and barley for barley, it should be measure for measure, but there is nothing wrong with selling barley for wheat, hand to hand, giving more barley than wheat, but no credit is allowed. And when you sell dates for dates, it should be measure for measure" And he mentioned salt, "measure for measure, and whoever gives more or asks for more has engaged in Riba. (Using translation from Nasāʾī 4563)
عَنْ عُبَادَةَ بْنِ الصَّامِتِ وَكَانَ بَدْرِيًّا وَكَانَ بَايَعَ رَسُولَ اللهِ ﷺ أَنْ لَا يَخَافَ فِي اللهِ لَوْمَةَ لَائِمٍ أَنَّ عُبَادَةَ بْنَ الصَّامِتِ قَامَ خَطِيبًا فَقَالَ أَيُّهَا النَّاسُ إِنَّكُمْ قَدْ أَحْدَثْتُمْ بُيُوعًا لَا أَدْرِي مَا هِيَ أَلَا إِنَّ الذَّهَبَ بِالذَّهَبِ وَزْنًا بِوَزْنٍ تِبْرُهَا وَعَيْنُهَا وَإِنَّ الْفِضَّةَ بِالْفِضَّةِ وَزْنًا بِوَزْنٍ تِبْرُهَا وَعَيْنُهَا وَلَا بَأْسَ بِبَيْعِ الْفِضَّةِ بِالذَّهَبِ يَدًا بَيْدٍ وَالْفِضَّةُ أَكْثَرُهُمَا وَلَا تَصْلُحُ نَسِيئَةً أَلَا إِنَّ الْبُرَّ بِالْبُرِّ وَالشَّعِيرَ بِالشَّعِيرِ مُدْيًا بِمُدْيٍ وَلَا بَأْسَ بِبَيْعِ الشَّعِيرِ بِالْحِنْطَةِ يَدًا بَيْدٍ وَالشَّعِيرُ أَكْثَرُهُمَا وَلَا يَصْلُحُ نَسِيئَةً أَلَا وَإِنَّ التَّمْرَ بِالتَّمْرِ مُدْيًا بِمُدْيٍ حَتَّى ذَكَرَ الْمِلْحَ مُدْيًا بِمُدْيٍ فَمَنْ زَادَ أَوِ اسْتَزَادَ فَقَدْ أَرْبَى