He informed him that he asked Saad bin Abu Waqqas about exchanging white wheat for unhusked barley. Saad asked him, "Which of the two is superior?"He replied, "The white wheat."So Saad forbade him from doing so and said, "I heard the Messenger of Allah ﷺ being asked about exchanging fresh dates for dried dates. He asked, 'Do fresh dates decrease in volume when they dry?' They said, 'Yes.' So he forbade that."
حدثنا علي بن محمد حدثنا وكيع وإسحق بن سليمان قالا حدثنا مالك بن أنس عن عبد الله بن يزيد مولى الأسود بن سفيان أن
أخبره أنه سأل سعد بن أبي وقاص عن اشتراء البيضاء بالسلت فقال له سعد أيتهما أفضل قال البيضاء فنهاني عنه وقال إني سمعت رسول الله ﷺ سئل عن اشتراء الرطب بالتمر فقال أينقص الرطب إذا يبس قالوا نعم فنهى عن ذلك
[Its chain is hasan] Abu Dawud narrated it in "Sales," chapter on selling fresh dates for dried dates, hadith no. 3359, from the hadith of Malik through this route, and it is found in the Muwatta (Yahya's version), 2/624. Tirmidhi graded it sahih, hadith no. 1225, as did Ibn Jarud, hadith no. 657, along with Hakim, 2/38, 39, and Dhahabi.