It is narrated from Nafi‘ that Ibn ‘Umar (may Allah be pleased with them) said: Do not sell gold for gold except equal for equal, and do not make one more than the other; (similarly) do not sell silver for silver except equal for equal, and do not make one more than the other.
Hadith Referenceمسند الإمام الشافعي / كتاب البيوع / 1388
Hadith Takhrijصحيح من قول عمر بن الخطاب اخرجه البيهقى 279/5 - وفى المعرفة السنن والآثار له (3373)۔ وعبد الرزاق (14562) - والطحاوى فى شرح معانی الآثار : (70/4)۔