The Messenger of Allah ﷺ said, "Gold for silver is usury unless it is exchanged hand to hand, wheat for wheat is usury unless it is exchanged hand to hand, dates for dates is usury unless it is exchanged hand to hand, and barley for barley is usury unless it is exchanged hand to hand."
حدثنا عبد الله بن مسلمة القعنبي عن مالك عن ابن شهاب عن مالك بن أوس
قال رسول الله ﷺ الذهب بالورق ربا إلا هاء وهاء والبر بالبر ربا إلا هاء وهاء والتمر بالتمر ربا إلا هاء وهاء والشعير بالشعير ربا إلا هاء وهاء
Bukhari narrated it in the Book of Sales, Chapter on the sale of barley for barley, no. 2174, from the hadith of Malik through this route, and Muslim narrated it, no. 1586, from the hadith of Ibn Shihab Zuhri through this route.