What is the ruling on purchasing gold in installments with staggered payments, and choosing the item upon completion of a certain amount, without pre-determining the item?

For gold to be sold for gold or for currency, it is a condition that possession be taken in the same session (majlis), because currencies have the rulings of gold and silver.

It is not permissible to sell gold on installment, whether the gold remains with the seller or is taken by the buyer.

If the buyer pays installments to the seller to purchase gold later: 1. It is permissible if the money is held by the seller as a trust (amanah) and he does not dispose of it. 2. It is not permissible if the seller disposes of the money, because it then becomes a loan, and it is not permissible to combine a loan and a sale.

Therefore, the buyer is advised to keep his money himself to avoid falling into usury (riba).