What is the ruling on selling gold on credit in Algeria, and what is the ruling on selling gold inlaid with crystal, where the weight of the crystal is included in the weight of the gold, and what is the ruling on selling used gold?

The aforementioned transaction—buying gold in installments without precise determination of the duration or the installment value—is likely to be a sale of gold on credit, which is forbidden by the majority of scholars. It also contains another prohibition, which is the uncertainty of the debt's maturity.

As for selling gold with banknotes and precious stones, there is no harm in it if people commonly agree to it and are satisfied with it. Selling used gold is permissible, and when selling it for circulating currency, it is not obligatory to sell it at its daily price; rather, the determining factor is what the buyer and seller agree upon, based on the saying of the Prophet, peace and blessings be upon him: "Gold for gold, silver for silver, like for like, equal for equal, hand to hand. If these types differ, then sell as you wish, provided it is hand to hand."

However, when exchanging used gold for new gold, there must be equality in weight.