Mukhtasar Bukhari

Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrates that Sayyiduna Bilal (may Allah be pleased with him) brought good quality dates of the "Barni" type to the Noble Prophet (peace and blessings of Allah be upon him). The Noble Prophet (peace and blessings of Allah be upon him) asked him: "Where did you get these from?" He replied: "We had some inferior dates, so we exchanged two sa’ of those for one sa’ of these dates so that we could feed them to the Noble Prophet (peace and blessings of Allah be upon him)." Upon hearing this, the Noble Prophet (peace and blessings of Allah be upon him) said: "Alas! Alas! This is pure usury; do not do this. Rather, when you want to buy (good dates), sell (the inferior dates) for something else, then buy (the good dates) with that." (This same hadith is also in Sahih Muslim with another chain, in which there are the words: "Return it.")