Sunan Ibn Majah, Chapter: The Chapters on Business Transactions

"I was with the Prophet (saw) on a military campaign, and he said to me: 'Will you sell this camel of yours for a Dinar?' I said: 'O Messenger of Allah, it is yours when I get to Al-Madinah.' He said: 'Then sell it for two Dinar, may Allah forgive you.' And he kept increasing the price for me, saying: 'May Allah forgive you,' each time, until the amount reached twenty Dinar. When I came to Al-Madinah, I took hold of the camel's head and brought it to the Prophet (saw) and he said: 'O Bilal, give him twenty Dinar from the spoils of war.' And he said: 'Take your camel away and go to your people with it.'"