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.