Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "A dinar for a dinar and a dirham for a dirham, with no excess between them." Sayyiduna Abdullah (may Allah be pleased with them both), accompanied by Nafi' (may Allah have mercy on him), walked and came to Abu Sa'id al-Khudri (may Allah be pleased with him) and asked him. He said: My eyes saw and my ears heard the Messenger of Allah (peace and blessings be upon him) saying: "A dinar for a dinar and a dirham for a dirham, with equal weight; with equal weight there shall be no excess between them, and what is in hand shall not be sold for what is deferred."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10489