Imam Malik's Muwatta, Chapter: Business Transactions

Yahya related to me from Malik that Yahya ibn Said heard Jamil ibn Abd ar-Rahman the Muadhdhin say to Said ibn al-Musayyab, "I am a man who buys whatever Allah wills of the receipts for the provisions which people are offered at al-Jar. I want to take payment for goods that I guarantee to deliver at a future date." Said said to him, "Do you intend to settle these things with receipts for provisions you have bought?" He said, "Yes." So he forbade that. Malik said, "The generally agreed on way of doing things among us in which there is no dispute, about buying food - wheat, barley, durra-sorghum, pearl millet, or any pulse or anything resembling pulses on which zakat is obliged, or condiments of any sort - oil, ghee, honey, vinegar, cheese, sesame oil, milk and so on, is that the buyer should not re-sell any of that until he has taken possession and complete delivery of it.