Sahih Muslim 1586 a
Malik b. Aus b. al-Hadathan reported:
I came saying who was prepared toexchange dirhams (for my gold), whereupon Talha b. Ubaidullah (Allah be pleased with him) (as he was sitting with 'Umar b. Khattib) said: Show us your gold and then come to us (at a later time). When our servant would come we would give you your silver (dirhams due to you). Thereupon 'Umar b. al-Khattib (Allah be pleased with him) said: Not at all. By Allah, either give him his silver (coins). or return his gold to him, for Allah's Messenger (ﷺ) said: Exchange of silver for gold (has an element of) interest in it. except when (it is exchanged) on the spot;and wheat for wheat is an interest unless both are handed over on the spot: barley for barley is interest unless both are handed over on the spot; dates for dates is interest unless both are handed over on the Spot.
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا لَيْثٌ، ح وَحَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَخْبَرَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ مَالِكِ بْنِ أَوْسِ بْنِ الْحَدَثَانِ، أَنَّهُ قَالَ أَقْبَلْتُ أَقُولُ مَنْ يَصْطَرِفُ الدَّرَاهِمَ فَقَالَ طَلْحَةُ بْنُ عُبَيْدِ اللَّهِ وَهُوَ عِنْدَ عُمَرَ بْنِ الْخَطَّابِ أَرِنَا ذَهَبَكَ ثُمَّ ائْتِنَا إِذَا جَاءَ خَادِمُنَا نُعْطِكَ وَرِقَكَ ‏.‏ فَقَالَ عُمَرُ بْنُ الْخَطَّابِ كَلاَّ وَاللَّهِ لَتُعْطِيَنَّهُ وَرِقَهُ أَوْ لَتَرُدَّنَّ إِلَيْهِ ذَهَبَهُ فَإِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ الْوَرِقُ بِالذَّهَبِ رِبًا إِلاَّ هَاءَ وَهَاءَ وَالْبُرُّ بِالْبُرِّ رِبًا إِلاَّ هَاءَ وَهَاءَ وَالشَّعِيرُ بِالشَّعِيرِ رِبًا إِلاَّ هَاءَ وَهَاءَ وَالتَّمْرُ بِالتَّمْرِ رِبًا إِلاَّ هَاءَ وَهَاءَ‏"‏ ‏.‏