(81) باب بَيْعِ الذَّهَبِ بِالْوَرِقِ يَدًا بِيَدٍ
Narrated `Abdur-Rahman bin Abu Bakra:
that his father said, "The Prophet (ﷺ) forbade the selling of gold for gold and silver for silver except if they are equivalent in weight, and allowed us to sell gold for silver and vice versa as we wished."
Reference: Sahih al-Bukhari 2182
In-book reference: Book 34, Hadith 130
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 34, Hadith 388