وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ عَنْ جَدِّهِ، مَالِكِ بْنِ أَبِي عَامِرٍ أَنَّ عُثْمَانَ بْنَ عَفَّانَ، قَالَ قَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ لاَ تَبِيعُوا الدِّينَارَ بِالدِّينَارَيْنِ وَلاَ الدِّرْهَمَ بِالدِّرْهَمَيْنِ ‏"‏ ‏.‏

Yahya related to me from Malik that he had heard from hisgrandfather, Malik ibn Abi Amir that Uthman ibn Affan said, "TheMessenger of Allah, may Allah bless him and grant him peace, said tome, 'Do not sell a dinar for two dinars nor a dirham for two dirhams.'" Translation Not Available

Book reference: Muwatta Imam Malik Book 31 Hadith 1323
Web reference: Muwatta Imam Malik Book 31 Hadith 32