Musnad Ahmad 773:9

Abu Kamil narrated to us, Sa'id ibn Zayd narrated to us, al-Zubayr ibn al-Khirrit narrated to us, Abu Labid narrated to us, from 'Urwah ibn Abi al-Ja'd al-Bariqi, who said: Some livestock (brought for sale) were presented to the Prophet, may Allah bless him and grant him peace. He gave me a dinar and said: "O 'Urwah, go to the livestock, and buy a sheep for us." I went to the livestock and bargained with its owner, and I bought two sheep from him for a dinar. I came driving them—or he said: leading them—and a man met me and bargained with me, so I sold him one sheep for a dinar. I came with the dinar and brought him the sheep, and I said: "O Messenger of Allah, this is your dinar and this is your sheep." He said: "And how did you do?" He said: So I told him the story. He said: "O Allah, bless him in the transaction of his right hand." I have seen myself standing at the marketplace of Kufa, and I would make a profit of forty thousand before I reached my family. And he used to buy slave girls and sell them.