It was narrated from 'Abdur-Rahman bin Abi Bakrah that his father said:
"The Messenger of Allah forbade us from selling silver for silver unless it was of equal amounts, or selling gold for gold unless it was of equal amounts. The messenger of Allah said: 'Sell gold for silver however you want, and silver for gold however you want."'
وَعَنْ عُبَادَةَ بْنِ اَلصَّامِتِ - رضى الله عنه - قَالَ: قَالَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -{ اَلذَّهَبُ بِالذَّهَبِ, وَالْفِضَّةُ بِالْفِضَّةِ, وَالْبُرُّ بِالْبُرِّ, وَالشَّعِيرُ بِالشَّعِيرِ…
وَعَنْ أَبِي هُرَيْرَةَ - رضى الله عنه - قَالَ: قَالَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -{ اَلذَّهَبُ بِالذَّهَبِ وَزْناً بِوَزْنٍ مِثْلًا بِمِثْلٍ، وَالْفِضَّةُ بِالْفِضَّةِ وَزْناً بِوَزْنٍ مِثْلًا بِمِثْلٍ…
"Silver for gold is Riba (usury) unless exchanged on the spot; wheat for wheat is Riba unless exchanged on the spot; barley for barley is Riba unless exchanged on the spot; and dates for dates is Riba unless exchanged on the spot."