Sahih Muslim Book 10, Hadith Number 3696.

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

Ibn ‘Umar (Allah be pleased with them) reported Allah’s Messenger (may peace be upon him) having forbidden Muzabana, and Muzabana is the selling of dry dates by measure for fresh dates and the selling of raisins by measure for grapes and selling of all Ports of fruits on the basis of calculation.