Muwatta Imam Malik Book of Business Transactions, Hadith 28

Yahya related to me from Malik that Yahya ibn Said said, "The Messenger of Allah, mayAllah bless him and grant him peace, ordered the two Sads to sell a vessel made of either gold or silver from the booty. They either sold each three units of weight for four units of weight of coins or each four units of weight for three units of weight or coins. The Messenger of Allah ﷺ said to them, 'You have taken usury, so return it.' "

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّهُ قَالَ أَمَرَ رَسُولُ اللَّهِ ﷺ السَّعْدَيْنِ أَنْ يَبِيعَا آنِيَةً مِنَ الْمَغَانِمِ مِنْ ذَهَبٍ أَوْ فِضَّةٍ فَبَاعَا كُلَّ ثَلاَثَةٍ بِأَرْبَعَةٍ عَيْنًا أَوْ كُلَّ أَرْبَعَةٍ بِثَلاَثَةٍ عَيْنًا فَقَالَ لَهُمَا رَسُولُ اللَّهِ ﷺ " أَرْبَيْتُمَا فَرُدَّا