Malik related to me from Zayd ibn Aslam that his father said,"Abdullah and Ubaydullah, the sons of Umar ibn al-Khattab went outwith the army to Iraq. On the way home, they passed by Abu Musa al-Ashari who was the amir of Basra. He greeted them and made themwelcome, and told them that if there was anything he could do to helpthem, he would do it. Then he said, 'There is some of the property ofAllah which I want to send to the amir al-muminin, so I will lend itto you, and you can buy wares from Iraq and sell them in Madina. Thengive the principal to the amir al-muminin, and you keep the profit.'They said that they would like to do it, and so he gave them the moneyand wrote to Umar ibn al-Khattab to take the money from them. Whenthey came to sell they made a profit, and when they paid the principalto Umar he asked, 'Did he lend everyone in the army the like of whathe lent you?' They said, 'No.' Umar ibn al-Khattab said, 'He made youthe loan, because you are the sons of the amir al-muminin, so pay theprincipal and the profit.' Abdullah was silent. Ubaydullah said, 'Youdo not need to do this, amir al-muminin. Had the principal decreasedor been destroyed, we would have guaranteed it.' Umar said, 'Pay it.'Abdullah was silent, and Ubaydullah repeated it. A man who was sittingwith Umar said, 'Amir al-muminin, better that you make it a qirad.'Umar said, 'I have made it qirad.' Umar then took the principal andhalf of the profit, and Abdullah and Ubaydullah, the sons of Umar ibnal-Khattab took half of the profit."
USC-MSA web (English) reference: Book 32, Hadith 1
Arabic reference: Book 32, Hadith 1389