Sahih Muslim Book 10, Hadith Number 3677.

Chapter : It is forbidden to sell fresh dates against dry dates, except in case of al-Araya.

Abu Huraira (Allah be pleased with him) reported Allah’s Messenger (may peace be upon him) as saying: Do not buy the fruit until their condition is clear, and do not buy the fresh dates. A hadith like this has been reported by Ibn ‘Umar through another chain of transmitters.