It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "One dinar is equal to one dinar, and one dirham is equal to one dirham; there is no superiority among them."
Hadith Referenceالسنن المأثورة / باب في البيوع / 212
Hadith Takhrijصحیح مسلم، المساقاة، باب الصرف وبيع الذهب بالورق نقدا، رقم : 1588 ۔