I asked Bara bin Azib and Zayd bin Arqam about currency exchange, and each one of them said, "This one is better than me." Both of them said, "The Messenger of Allah ﷺ forbade the sale of gold for silver on credit."
سألت البراء بن عازب وزيد بن أرقم عن الصرف، وكل واحد منهما يقول: هذا خير مني، فكلاهما يقول: نهي رسول الله ﷺ عن بيع الذهب بالورق دينا.
Bukhari related it in the Book of Sales (2180, 2181), and Muslim in the Book of Cultivation (1589), both from the hadith of Shubah, from Habib bin Abu Thabit, who said, "I heard Abu Minhal," and mentioned it.