Sahih Muslim Book 10, Hadith Number 3683.

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

Zaid b Thabit (Allah be pleased with him) reported that Allah’s Messenger (may peace be upon him) gave concession in case of al-‘ariyya transactions (for exchanging dates) for dates with measure. Yahya said: ‘Ariyya implies that a person should buy fresh dates on the tree for his family to eat against a measure of dry dates.