It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) forbade (two types of transactions): muzabanah and muhaqalah. Muzabanah is when fresh dates on the trees are bought in exchange for dried dates, and muhaqalah is when land is leased out in exchange for a specified amount of wheat.

And with the same chain of narration (from Sayyiduna Ibn Umar, may Allah be pleased with them both), it is narrated that the Messenger of Allah, peace and blessings be upon him, forbade muzabanah (and muzabanah is that) dates on the tree are sold by measure in exchange for dried dates, and grapes on the vine are sold by measure in exchange for dried grapes.