Abu Salih Dhakwan narrates that he asked Sayyiduna Ibn Abbas (may Allah be pleased with them both) about selling gold for silver, and he said: "It is permissible even with increase or decrease, provided it is hand to hand." Abu Salih said: Then I asked Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) about this, and he said: "It is forbidden except like for like." So I told Abu Sa'id what Ibn Abbas had said, and I told Ibn Abbas what Abu Sa'id al-Khudri had said. Then the two of them met while I was with them, and Abu Sa'id al-Khudri began (the conversation), saying: O Ibn Abbas, what is this fatwa that you give people about selling gold for silver, ordering them to buy it with decrease or increase, hand to hand? Ibn Abbas said: I am not the earliest of you in companionship with the Messenger of Allah (peace and blessings be upon him), and here are Sayyiduna Zayd bin Arqam and Sayyiduna al-Bara' bin Azib (may Allah be pleased with them both), who say: We heard the Prophet (peace and blessings be upon him).
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 435