سنن ابن ماجه

It was narrated from 'Abdullah bin Yazid, the freed slave of Al-Aswad bin Sufyan, that : Zaid, Abu 'Ayyash, the freed slave of Bani Zuhrah, told him that he asked Sa'd bin Abu Waqqas about buying wheat with barley. Sa'd said to him: "Which of them is better?" He said: "Wheat." He told him not to do that and said: "I heard the Messenger of Allah (ﷺ) being asked about buying fresh dates with dried dates, and he said: 'Do fresh dates decrease in weight when they become dry?' They said: 'Yes.' So he told them not to do that."