"Zaid, Abu Ayyash asked Sa'd regarding white wheat in exchange for barley: which of them was better ? He said the white, then he forbade that. Sa'd said: 'I heard the Messenger of Allah (ﷺ) being asked about selling dried dates for ripe dates and he said to those present: "Will the fresh dates shrink when they are dry ?" They said yes, so he forbade that.'"
حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا مَالِكُ بْنُ أَنَسٍ، عَنْ عَبْدِ اللَّهِ بْنِ يَزِيدَ، أَنَّ زَيْدًا أَبَا عَيَّاشٍ، سَأَلَ سَعْدًا عَنِ الْبَيْضَاءِ، بِالسُّلْتِ فَقَالَ أَيُّهُمَا أَفْضَلُ قَالَ الْبَيْضَاءُ . فَنَهَى عَنْ ذَلِكَ . وَقَالَ سَعْدٌ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُسْأَلُ عَنِ اشْتِرَاءِ التَّمْرِ بِالرُّطَبِ فَقَالَ لِمَنْ حَوْلَهُ أَيَنْقُصُ الرُّطَبُ إِذَا يَبِسَ . قَالُوا نَعَمْ . فَنَهَى عَنْ ذَلِكَ .
Tirmizi
The Book on Business • Hadith 1231