I asked Ibn Umar and Ibn Abbas (Allah be pleased with them) about the conversion of gold with gold but they did not find any harm in that. I was sitting in the company of Abd Sa'id al-Khudri (Allah be pleased with him) and asked him about this exchange, and he said: Whatever is addition is an' interest. I refused to accept it on account of their statement (statement of Ibn 'Abbas and Ibn 'Umar). He said: I am not narrating to you except what I heard from Messenger of Allah ﷺ. There came to him the owner of a date-palm with one sa' of fine dates, and the dates of Allah's Apostle ﷺ were of that colour. Allah's Apostle ﷺ said to him: Where did you get these dates? I went with two sa's of (inferior dates) and bought one sa' of (these fine dates), for that is the prevailing price (of inferior dates) in the market and that is the price (of the fine quality of dates in the market), whereupon Messenger of Allah ﷺ said: Woe be upon you! You have dealt in interest, when you decide to do it (i. e. exchange superior quality of dates for inferior quality) ; so you should sell your dates for another commodity (or currency) and then with the help of that commodity buy the dates you like. Abu Sa'ad said: When dates are exchanged for dates (with different qualities) there is the possibility (of the element of) interest (creeping into that) or when gold is exchanged for gold having different qualities. I subsequently came to Ibn 'Umar and he forbade me (to do it), but I did not come to Ibn 'Abbas; (Allah be pleased with them). He (the narrator) said: Abu as-Sahba' narrated to me: He asked Ibn Abbas (Allah be pleased with them) in Mecca, and he too disapproved of it. (Using translation from Muslim 1594d)   

عَنِ الصَّرْفِ فَلَمْ يَرَيَا بِهِ بَأْسًا وَإِنِّي لَقَاعِدٌ عِنْدَ أَبِي سَعِيدٍ الْخُدْرِيِّ فَسَأَلْتُهُ عَنِ الصَّرْفِ فَقَالَ مَا زَادَ فَهُوَ رِبًا فَأَنْكَرْتُ ذَلِكَ لِقَوْلِهِمَا فَقَالَ لَا أُحَدِّثُكُمْ إِلَّا مَا سَمِعْتُ مِنْ رَسُولِ اللهِ ﷺ جَاءَهُ صَاحِبُ نَخْلَةٍ بِصَاعٍ مِنْ تَمْرٍ طَيِّبٍ وَكَانَ تَمْرُ النَّبِيِّ ﷺ هُوَ الدُّونَ فَقَالَ لَهُ النَّبِيُّ ﷺ أَنَّى لَكَ هَذَا؟ قَالَ انْطَلَقْتُ بِصَاعِي وَاشْتَرَيْتُ بِهِ هَذَا الصَّاعَ فَإِنَّ سِعْرَ هَذَا بِالسُّوقِ كَذَا وَسِعْرَ هَذَا بِالسُّوقِ كَذَا فَقَالَ لَهُ رَسُولُ اللهِ ﷺ أَرْبَيْتَ إِذَا أَرَدْتَ ذَلِكَ فَبِعْ تَمْرَكَ بِسِلْعَةٍ ثُمَّ اشْتَرِ بِسِلْعَتِكَ أِيَّ تَمْرٍ شِئْتَ فَقَالَ أَبُو سَعِيدٍ فَالتَّمْرُ بِالتَّمْرِ أَحَقُّ أَنْ يَكُونَ رِبًا وَالْفِضَّةُ بِالْفِضَّةِ قَالَ فَأَتَيْتُ ابْنَ عُمَرَ بَعْدُ فَنَهَانِي وَلَمْ آتِ ابْنَ عَبَّاسٍ قَالَ فَحَدَّثَنِي أَبُو الصَّهْبَاءِ أَنَّهُ سَأَلَ ابْنَ عَبَّاسٍ عَنْهُ فَكَرِهَهُ  

[Machine] "That the Prophet ﷺ forbade it, so I forbid you from it."  

أَنَّ النَّبِيَّ ﷺ نَهَى عَنْهُ فَأَنَا أَنْهَاكُمْ عَنْهُ  

[Machine] There is no harm if the man marries her, and Abdullah was in charge of the treasury, and he used to sell the waste of the treasury, giving more and taking less. Until he arrived in the city, and asked the companions of Muhammad, ﷺ , and they said, "This man is not allowed to marry this woman, and silver is not accepted except by weight." When Abdullah arrived, he went to the man but did not find him, and he found his people and said, "Indeed, the one I gave the fatwa for said that it is not allowed." They said, "She has scattered her belly." He said, "Even if he came to the market, he said, 'O people of the market, indeed, the one I used to sell to you is not allowed. Silver cannot be exchanged for silver except by weight.'"  

لَا بَأْسَ فَتَزَوَّجَهَا الرَّجُلُ وَكَانَ عَبْدُ اللهِ عَلَى بَيْتِ الْمَالِ وَكَانَ يَبِيعُ نِفَايَةَ بَيْتِ الْمَالِ يُعْطِي الْكَثِيرَ وَيَأْخُذُ الْقَلِيلَ حَتَّى قَدِمَ الْمَدِينَةَ فَسَأَلَ أَصْحَابَ مُحَمَّدٍ ﷺ فَقَالُوا لَا يَحِلُّ لِهَذَا الرَّجُلِ هَذِهِ الْمَرْأَةُ وَلَا تَصْلُحُ الْفِضَّةُ إِلَّا وَزْنًا بِوَزْنٍ فَلَمَّا قَدِمَ عَبْدُ اللهِ انْطَلَقَ إِلَى الرَّجُلِ فَلَمْ يَجِدْهُ وَوَجَدَ قَوْمَهُ فَقَالَ إِنَّ الَّذِي أَفْتَيْتُ بِهِ صَاحِبَكُمْ لَا يَحِلُّ فَقَالُوا إِنَّهَا قَدْ نَثَرَتْ لَهُ بَطْنَهَا قَالَ وَإِنْ كَانَ وَأَتَى الصَّيَارِفَةَ فَقَالَ يَا مَعْشَرَ الصَّيَارِفَةِ إِنَّ الَّذِي كُنْتُ أُبَايِعُكُمْ لَا يَحِلُّ لَا تَحِلُّ الْفِضَّةُ بِالْفِضَّةِ إِلَّا وَزْنًا بِوَزْنٍ