It is narrated from Sayyiduna Rafi' bin Khadij and Sayyiduna Sahl bin Abi Hathmah (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) forbade muzabanah - and muzabanah is selling (fresh) dates (on the tree) for (dry) dates - except for the people of the 'araya, for they were given permission for it.
Hadith Referenceالمعجم الكبير للطبراني / باب الراء / 4410