Muwatta Imam Malik Book of Business Transactions, Hadith 82

Yahya related to me from Malik from Abu'z-Zinad from Busr ibn Said from Ubayd, Abu Salih, the mawla of as-Saffah that he said, "I sold drapery to the people of Dar Nakhla on credit. Then I wanted to go to Kufa, so they proposed that I reduce the price for them and they would pay me immediately . I asked Zayd ibn Thabit about that, and he said, 'I order you not to accept increase or to give to anybody.' "

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، عَنْ بُسْرِ بْنِ سَعِيدٍ، عَنْ عُبَيْدٍ أَبِي صَالِحٍ، مَوْلَى السَّفَّاحِ أَنَّهُ قَالَ بِعْتُ بَزًّا لِي مِنْ أَهْلِ دَارِ نَخْلَةَ إِلَى أَجَلٍ ثُمَّ أَرَدْتُ الْخُرُوجَ إِلَى الْكُوفَةِ فَعَرَضُوا عَلَىَّ أَنْ أَضَعَ عَنْهُمْ بَعْضَ الثَّمَنِ وَيَنْقُدُونِي فَسَأَلْتُ عَنْ ذَلِكَ زَيْدَ بْنَ ثَابِتٍ فَقَالَ لاَ آمُرُكَ أَنْ تَأْكُلَ هَذَا وَلاَ تُوكِلَهُ .