كتاب المساقاة
22  
The Book of Musaqah
(15)
Chapter: Exchange and Selling Gold for Silver on the spot
(15)
باب الصَّرْفِ وَبَيْعِ الذَّهَبِ بِالْوَرِقِ نَقْدًا ‏‏
Sahih Muslim 1588 c

Abu Huraira (Allah be pleased with him) reported Allah's Mess-., nger (ﷺ) as saying:

Gold is to be paid for by gold with equal weight, like for like, and silver is to be paid for by silver with equal weight, like for like. He who made an addition to it or demanded an addition dealt in usury.
حَدَّثَنَا أَبُو كُرَيْبٍ، وَوَاصِلُ بْنُ عَبْدِ الأَعْلَى، قَالاَ حَدَّثَنَا ابْنُ فُضَيْلٍ، عَنْ أَبِيهِ، عَنِ ابْنِ أَبِي نُعْمٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ الذَّهَبُ بِالذَّهَبِ وَزْنًا بِوَزْنٍ مِثْلاً بِمِثْلٍ وَالْفِضَّةُ بِالْفِضَّةِ وَزْنًا بِوَزْنٍ مِثْلاً بِمِثْلٍ فَمَنْ زَادَ أَوِ اسْتَزَادَ فَهُوَ رِبًا‏"‏ ‏.‏
Reference : Sahih Muslim 1588c
In-book reference : Book 22, Hadith 107
USC-MSA web (English) reference : Book 10, Hadith 3857
  (deprecated numbering scheme)