Muwatta 1953

Malik says of a man who buys goods with gold or silver, where the exchange on the day he bought was ten dirhams to a dinar, then takes them to another city and sells them on a cost-plus basis, or sells them where he bought them on a cost-plus basis at the exchange of the day he sold them: if he bought with dirhams and sold for dinars, or bought with dinars and sold for dirhams, and the goods have not been lost, the buyer has the option: if he wishes he takes them, and if he wishes he leaves them. If the goods are lost, the buyer owes the price at which the seller bought them, and the seller is credited with the profit on what he bought them for, as the buyer made profit on it. ¹

Belongs to the Muwatta, Book of Sales. Source: the Muwatta. Mentions Malik ibn Anas. Built on in the chapters on resale at cost plus profit (murabaha) and currency exchange (sarf).