From Sahih Muslim (Hadith 4066):
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as saying:Dates are to be paid for by dates, wheat by wheat, barley by barley, salt by salt, like for like, payment being made on the spot. He who made an addition or demanded an addition, in fact, dealt in usury except in case where their classes differ
Reference: Muslim 4066