From Sahih Muslim (Hadith 4084):
Abu Sa'id (Allah be pleased with him) reported:Dates were brought to Allah's Messenger (ﷺ), and he said: These dates are not like our dates, whereupon a man said: We sold two sa's of our dates (in order to get) one sa', of these (fine dates), whereupon Allah's Messenger (ﷺ) said: That is interest; so return (these dates of fine quality), and get your (inferior dates) ; then sell our dates (for money) and buy for us (with the help of money) such (fine dates)
Reference: Muslim 4084