Yahya related to me from Malik from Abu'z-Zinad from Busr ibnSaid from Ubayd, Abu Salih, the mawla of as-Saffah that he said, "Isold drapery to the people of Dar Nakhla on credit. Then I wanted togo to Kufa, so they proposed that I reduce the price for them and theywould pay me immediately . I asked Zayd ibn Thabit about that, and hesaid, 'I order you not to accept increase or to give to anybody.' "
USC-MSA web (English) reference: Book 31, Hadith 82
Arabic reference: Book 31, Hadith 1369