Muwatta Malik, Book 31, Hadith 1319 (In-Book) ⓘ

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, may Allah bless him and grant him peace, said to them, 'You have taken usury, so return it.' "

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