كتاب المساقاة
22  
The Book of Musaqah
(16)
Chapter: The Prohibition of selling silver for gold to be paid at a later date
(16)
باب النَّهْىِ عَنْ بَيْعِ الْوَرِقِ، بِالذَّهَبِ دَيْنًا ‏‏
Sahih Muslim 1589 b

Habib reported that he heard Abu Minhal as saying:

I asked al-Bara' b. Azib about the exchange of (gold for silver or vice versa), whereupon he said: you better ask Zaid b. Arqam for he knows more than I. So I asked Zaid but he said: You better ask al-Bara' for he knows more than I. Then both of them said: Allah's Messenger (ﷺ) forbade the sale of silver for gold when payment is to be made in future.
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ الْعَنْبَرِيُّ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ حَبِيبٍ، أَنَّهُ سَمِعَ أَبَا الْمِنْهَالِ، يَقُولُ سَأَلْتُ الْبَرَاءَ بْنَ عَازِبٍ عَنِ الصَّرْفِ، فَقَالَ سَلْ زَيْدَ بْنَ أَرْقَمَ فَهُوَ أَعْلَمُ ‏.‏ فَسَأَلْتُ زَيْدًا فَقَالَ سَلِ الْبَرَاءَ فَإِنَّهُ أَعْلَمُ ثُمَّ قَالاَ نَهَى رَسُولُ اللَّهِ صلى الله عليه وسلم عَنْ بَيْعِ الْوَرِقِ بِالذَّهَبِ دَيْنًا.
Reference : Sahih Muslim 1589b
In-book reference : Book 22, Hadith 111
USC-MSA web (English) reference : Book 10, Hadith 3860
  (deprecated numbering scheme)