Abu Qilabah narrates from Abu al-Ash'ath (may Allah have mercy on him): We were on a military expedition, and our commander was Sayyiduna Mu'awiyah (may Allah be pleased with him). We obtained gold and silver as spoils. Sayyiduna Mu'awiyah (may Allah be pleased with him) ordered a man to sell it to the people against their stipends, and the people hastened to buy it. Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) forbade them from it, so the people returned the goods, and a man complained to Sayyiduna Mu'awiyah (may Allah be pleased with him). Sayyiduna Mu'awiyah (may Allah be pleased with him) delivered a sermon and said: People narrate hadiths from the Messenger of Allah (peace and blessings be upon him) in which they lie about the Messenger of Allah (peace and blessings be upon him), while we did not hear those hadiths from him (peace and blessings be upon him). Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) stood up and said: We will narrate hadiths from the Messenger of Allah (peace and blessings be upon him) even if Mu'awiyah dislikes it. The Messenger of Allah (peace and blessings be upon him) said: "Do not sell gold for gold, silver for silver, wheat for wheat, barley for barley, salt for salt, or dates for dates, except equal for equal, kind for kind."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10481