Sahih Muslim Book 10, Hadith Number 3697.

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 implies the selling of dry dates for fresh dates on the tree with a definite measure (making it clear) that in case it increases, it belongs to me and if it is less, it is my responsibility.