Musannaf Ibn Abi Shaybah

Hazrat Abdullah bin Yazid Ansari sent his servant with four thousand dirhams; the servant went to Isfahan and engaged in trade until he had twenty thousand dirhams. Then the servant passed away. It was said to Hazrat Abdullah (may Allah be pleased with him) that the servant used to mix usury in the trade. He (may Allah have mercy on him) took back only the original four thousand and left the remaining money, not taking it.