What is the ruling on my purchasing ready-mix concrete for a company, with specified characteristics and from a specific seller, on condition that I pay its price myself, and then the company reimburses me the full amount plus a daily profit that increases with the duration, knowing that the concrete does not come into my possession?

The aforementioned transaction is invalid because the price is undefined and variable. It can be corrected by specifying the price in the contract between the buyer and the company, and a separate contract with the manufacturing company (parallel istisna' - manufacturing contract). The Islamic Fiqh Academy has permitted this, and Shariah Standard No. (11) states the permissibility for an institution to conclude an istisna' contract with a manufacturer and sell to another party through a parallel istisna' contract, for products with the same specifications, and for a deferred period after the first istisna' period, provided that the two contracts are not linked.