Hadith 1320
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 his grandfather, Malik ibn Abi Amir that Uthman ibn Affan said, "The Messenger of Allah, may Allah bless him and grant him peace, said to me, 'Do not sell a dinar for two dinars nor a dirham for two dirhams
Sahih (Salim al-Hilali)
Muwatta Malik 1320 · Book 31, Hadith 31