Sunan an-Nasa'i, Volume 5, Book 44, Hadith 4562 (DarusSalam) ⓘ
Umar bin Al-Khattab said: "The Messenger of Allah said: '(Exchanging) gold for silver is Riba unless it is done on the spot. (Exchanging) dates for dates is Riba unless it is done on the spot. (Exchanging) wheat for wheat is Riba unless it is done on the spot. (Exchanging) barley is Riba unless it is done on the spot."'
أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ مَالِكِ بْنِ أَوْسِ بْنِ الْحَدَثَانِ، أَنَّهُ سَمِعَ عُمَرَ بْنَ الْخَطَّابِ، يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الذَّهَبُ بِالْوَرِقِ رِبًا إِلاَّ هَاءَ وَهَاءَ وَالتَّمْرُ بِالتَّمْرِ رِبًا إِلاَّ هَاءَ وَهَاءَ وَالْبُرُّ بِالْبُرِّ رِبًا إِلاَّ هَاءَ وَهَاءَ وَالشَّعِيرُ بِالشَّعِيرِ رِبًا إِلاَّ هَاءَ وَ هَاءَ " .
also referenced under: Hadith 4558 (Reference) & Book 44, Hadith 110 (In-Book)