Sahih al-Bukhari 2302, 2303

Narrated Abu Sa`id Al-Khudri and Abu Huraira:Allah's Messenger (ﷺ) employed someone as a governor at Khaibar. When the man came to Medina, he brought with him dates called Janib. The Prophet (ﷺ) asked him, "Are all the dates of Khaibar of this kind?" The man replied, "(No), we exchange two Sa's of bad dates for one Sa of this kind of dates (i.e. Janib), or exchange three Sa's for two." On that, the Prophet (ﷺ) said, "Don't do so, as it is a kind of usury (Riba) but sell the dates of inferior quality for money, and then buy Janib with the money". The Prophet said the same thing about dates sold by weight. (See Hadith No. 506).