We used to be given mixed dates (from the booty) and used to sell (barter) two Sas of those dates) for one Sa (of good dates). The Prophet ﷺ said (to us), "No (bartering of) two Sas for one Sa nor two Dirhams for one Dirham is permissible", (as that is a kind of usury). (See Hadith No. 405). (Using translation from Bukhārī 2080)
كُنَّا نُرْزَقُ تَمْرَ الْجَمْعِ عَلَى عَهْدِ رَسُولِ اللهِ ﷺ وَهُوَ الْخِلْطُ مِنَ التَّمْرِ فَكُنَّا نَبِيعُ الصَّاعَيْنِ بِالصَّاعِ فَقَالَ يَعْنِي النَّبِيَّ ﷺ لَا وَلَا الدِّرْهَمَ بِالدِّرْهَمَيْنِ