From Sahih Bukhari (Hadith 2202):
Narrated Abu Sa`id Al-Khudri and Abu Huraira:Allah's Messenger (ﷺ) appointed somebody as a governor of Khaibar. That governor brought to him an excellent kind of dates (from Khaibar). The Prophet (ﷺ) asked, "Are all the dates of Khaibar like this?" He replied, "By Allah, no, O Allah's Messenger (ﷺ)! But we barter one Sa of this (type of dates) for two Sas of dates of ours and two Sas of it for three of ours." Allah's Messenger (ﷺ) said, "Do not do so (as that is a kind of usury) but sell the mixed dates (of inferior quality) for money, and then buy good dates with that money
Reference: Bukhari 2202