From Sahih Bukhari (Hadith 2181):
Narrated Abu Al-Minhal:I asked Al-Bara' bin `Azib and Zaid bin Arqam about money exchanges. Each of them said, "This is better than I," and both of them said, "Allah's Messenger (ﷺ) forbade the selling of silver for gold on credit
Reference: Bukhari 2181