Beware! Beware! This is definitely usury! This is definitely usury! Do not do so, but if you want to buy (a superior kind of dates) sell the inferior dates for money, and then buy the superior kind of dates with that money

Bilāl came to the Prophet (may Allah's peace and blessings be upon him) with some good Burni dates. The Prophet (may Allah's peace and blessings be upon him) was surprised at their good quality and asked him: "From where did you get these dates?" Bilāl responded: "I had some other dates of less quality so I sold two Sā‘s of them for one Sā‘ of these Barni dates (in an exchange) to let the Prophet (may Allah's peace and blessings be upon him) eat from them.

The Prophet was greatly disturbed by this deal and he expressed his annoyance because any form of disobedience in his sight was the greatest calamity. So he explained himself and said: "What you did Bilāl is the prohibited usury in essence. So, never do it. If you want to exchange something of bad quality, sell it first and then buy with its money something of better quality. This is the permissible way to do this kind of transaction in order to stay away from impermissible ways.