عَنِ ابْنِ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ لَا تَبِيعُوا الدِّينَارَ بِالدِّينَارَيْنِ وَلَا الدِّرْهَمَ بِالدِّرْهَمَيْنِ وَلَا الصَّاعَ بِالصَّاعَيْنِ فَإِنِّي أَخَافُ عَلَيْكُمُ الرَّمَاءَ وَالرَّمَاءُ هُوَ الرِّبَا فَقَامَ إِلَيْهِ رَجُلٌ فَقَالَ يَا رَسُولَ اللَّهِ أَرَأَيْتَ الرَّجُلَ يَبِيعُ الْفَرَسَ بِالْأَفْرَاسِ وَالنَّجِيبَةَ بِالْإِبِلِ قَالَ لَا بَأْسَ إِذَا كَانَ يَدًا بِيَدٍ
It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: Do not sell one dinar for two dinars, nor one dirham for two dirhams, nor one sa’ for two sa’s, for I fear that you may fall into usury. A man stood up and said, “O Messenger of Allah! What is your ruling regarding a man selling one horse for several horses, or a she-camel for a camel?” He (peace and blessings be upon him) said: When it is hand to hand, there is no harm in it.