Sahih Muslim Book 10, Hadith Number 3694.

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

‘Abdullah (b. Umar) reported that Allah’s Apostle (may peace be upon him) forbade Muzabana, i.e. buying of fresh dates (on) the trees for dry dates by measure, and the buying of grapes for raisins by measure and the selling of field of corn for corn by measure.