Sahih Muslim Book 10, Hadith Number 3678.

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

Sa’id b. al-Musayyib said that Allah’s Messenger (may peace be upon him) forbade the transaction of Af Muzabana and Muhaqala. Muzabana means that fresh dates on the trees should be sold against dry dates. Muhaqala implies that the wheat in the ear should be sold against the wheat and getting the land on rent for the wheat (produced in it). He (the narrator) said that the Holy Prophet (may peace be upon him) had aid: Do not sell fresh fruits on the trees until their good condition becomes manifest, and do not sell fresh dates on the trees against dry dates. Salim said: Abdullah informed me on the authority of Zaid b. Thabit, Allah’s Messenger (may peace be upon him) having given concession afterwards in case of ariyya transactions by which dry dates can be exchanged with fresh dates, but he did not permit it in other cases.