Sahih Muslim Book 10, Hadith Number 3674.

Chapter : Prohibition of the sale of fruits until they are clearly in good condition.

Abu Bakhtari reported: I asked Ibn ‘Abbas (Allah be pleased with them) about the sale of dates. He said: Allah’s Messenger (may peace be upon him) forbade the sale of dates of the trees until one eats them or they are eaten (i.e. they are fit to be eaten) or until they are weighed (or measured). I said: What does it imply: “Until it is weighed”? Thereupon a person who was with him (Ibn Abbas) said: Until he is able to keep it with him (after plucking them).