It is narrated from Uthman (may Allah be pleased with him) that he stated: The Messenger of Allah (peace and blessings be upon him) said: "Do not sell one dinar for two dinars, nor one dirham for two dirhams."
Hadith Referenceمسند الإمام الشافعي / كتاب البيوع / 1386
Hadith Takhrijصحيح من غير هذا الطريق اخرجه مسلم ، البيوع ، الربا (1585)۔