Abu Sa'id and Abu Huraira told that God’s Messenger appointed a man over Khaibar and he brought him dates of a very fine quality. He asked him whether all the dates of Khaibar were like that, and he replied, “I swear by God that they are certainly not, Messenger of God. We take a sa‘ of this kind for two, and two for three." So he said, "Do not do so. Sell the lot for dirhams, then buy the very fine dates for dirhams." He said that it was the same when things were sold by weight.
‘Umar reported God's Messenger as saying, "Gold for gold is usury unless both hand over on the spot*; silver for silver is usury unless both hand over on the spot; wheat for wheat is usury unless both hand over on the spot; barley for barley is usury unless both hand over on the spot; dates for dates is usury unless both hand over on the spot."
(Bukhari and Muslim.)
*"the Arabic is ha’ waha’ meaning literally "take and take”.
Abu Sa'id said that Bilal brought the Prophet some barni* dates, and when he asked him where he had got them he replied, "I had some inferior dates, so I sold two sa's of them for a sa." He said, "Ah, the very essence of usury, the very essence of usury. Do not do so, but when you wish to buy, sell the dates in a separate transaction, then buy with what you get."
(Bukhari and Muslim.)
* A type of dates of the best quality, sweet and luscious, red tinged with yellow.