Sunan an-Nasa'i, Volume 5, Book 44, Hadith 4549 (DarusSalam) ⓘ

it was narrated that Sa'd said: "The Messenger of Allah was asked about (buying) fresh dates with dried dates, and he said to those who were around him: 'Will fresh dates decrease (in weight or volume) when they dry out?" they said Yes,' so he forbade that."

أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، قَالَ حَدَّثَنَا مَالِكٌ، قَالَ حَدَّثَنِي عَبْدُ اللَّهِ بْنُ يَزِيدَ، عَنْ زَيْدِ بْنِ عَيَّاشٍ، عَنْ سَعْدٍ، قَالَ سُئِلَ رَسُولُ اللَّهِ صلى الله عليه وسلم عَنِ التَّمْرِ بِالرُّطَبِ فَقَالَ لِمَنْ حَوْلَهُ ‏ "‏ أَيَنْقُصُ الرُّطَبُ إِذَا يَبِسَ ‏" ‏ ‏.‏ قَالُوا نَعَمْ ‏.‏ فَنَهَى عَنْهُ ‏.‏