Which of them is better? He replied: Soft and white kind of wheat. So he forbade him from it and said: I heard the Messenger of Allah (sawa) say, when he was asked about buying dry dates for fresh. The Messenger of Allah (sawa) said: Are fresh dates diminished when they become dry? The (the people) replied: Yes. So the Messenger of Allah ﷺ forbade that. Abu Dawud said: A similar tradition has also been transmitted by Isma'il b. Umayyah. (Using translation from Abū Dāʾūd 3359)   

سَمِعْتُ رَسُولَ اللهِ ﷺ يَسْأَلُ عَنِ اشْتِرَاءِ التَّمْرِ بِالرُّطَبِ قَالَ «أَيَنْقُصُ الرُّطَبُ إِذَا يَبِسَ؟» قَالُوا نَعَمْ فَنَهَى عَنْهُ