ENOfficial
Sa'd b. Abu Waqqas said he heard God's Messenger being asked about buying dry dates for fresh and asking whether the fresh dates were diminished when they became dry. On being told that they were, he forbade that. Malik, Tirmidhi, Abu Dawud, Nasa’i and Ibn Majah transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ سَعْدِ بْنِ أَبِي وَقَّاصٍ قَالَ: سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ سُئِلَ عَنْ شِرَاءِ التَّمْرِ بِالرُّطَبِ فَقَالَ: «أَيَنْقُصُ الرُّطَبُ إِذَا يَبِسَ؟» فَقَالَ: نَعَمْ فَنَهَاهُ عَنْ ذَلِكَ. رَوَاهُ مَالِكٌ وَالتِّرْمِذِيُّ وَأَبُو دَاوُدَ وَالنَّسَائِيُّ وَابْنُ مَاجَه
sunnah.com