Nafi' (may Allah have mercy on him) said: A man came to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) and narrated to him a hadith of Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him). Then Abu Sa'id came and stayed in this house. He (Ibn Umar) took me by the hand until we came to him, and Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: What is this man narrating from you? Sayyiduna Abu Sa'id (may Allah be pleased with him) said: My eyes saw and my ears heard — (Nafi' said:) I have not forgotten how he gestured with his finger as he said it — the Messenger of Allah (peace and blessings be upon him) forbade the sale of gold for gold and silver for silver except equal for equal, and said: "Do not make one exceed the other, and do not sell what is in hand for what is deferred."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10488