Malik bin Aws bin al-Hadathan (may Allah be pleased with him) said: I wanted to exchange money, and Talhah bin Ubaydullah (may Allah be pleased with him) said: I will exchange it for you, but (wait) until my treasurer returns from al-Ghabah. Malik (may Allah be pleased with him) said: Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Selling silver for silver, gold for gold, wheat for wheat and barley for barley is usury, except in a hand-to-hand exchange."
Thus it is in this narration: "silver for silver, gold for gold."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10510