Allah's Messenger (ﷺ) said, "Do not sell gold for gold unless equivalent in weight, and do not sell less amount for greater amount or vice versa; and do not sell silver for silver unless equivalent in weight, and do not sell less amount for greater amount or vice versa and do not sell gold or silver that is not present at the moment of exchange for gold or silver that is present.
Sahih al-Bukhari Book 34, Hadith 127
← Previous Hadith (Concerning exchange) that he heard Allah's Messenger (ﷺ) saying, "Do not sell gold for gold unless equal in weight, and do not sell silver unless equal in weight."

Sahih al-Bukhari Book 34, Hadith 126 Next Hadith → I heard Abu Sa`id Al-Khudri saying, "The selling of a Dinar for a Dinar, and a Dirham for a Dirham (is permissible)." I said to him, "Ibn `Abbas does not say the same." Abu Sa`id replied, "I asked Ibn `Abbas whether he had heard it from the Prophet (ﷺ) s or seen it in the Holy Book. Ibn `Abbas replied, "I do not claim that, and you know Allah's Messenger (ﷺ) better than I, but Usama informed me that the Prophet had said, 'There is no Riba (in money exchange) except when it is not done from hand to hand (i.e. when there is delay in payment).' "

Sahih al-Bukhari Book 34, Hadith 128