What is the ruling on investing money in housing projects and shopping centers that sell residential or commercial units before their construction, with a discount offered for cash payment, either through an immediate deduction from the total price or a discount from future installments?

It is permissible to sell apartments and shops before their construction, provided that their description removes any ambiguity, whether the price is paid immediately or deferred. This is known as an Istisna' contract (manufacturing contract). If the one who pays the full price receives a 10% discount, there is no harm in that. It is also permissible to buy land with an immediate or deferred price, because installment sales are permissible except in cases where the exchange of both countervalues is stipulated to occur in the same sitting.