What is the weight of gold that must be repaid: is it 13 grams, or 10 grams, if the weight of what was borrowed was 13 grams of gold mixed with copper, containing 3 grams of copper?

First: It is permissible to lend gold on the condition that an equal weight be returned. The borrower may return something better than what was taken, without prior stipulation or collusion. It is also permissible to return an alloy as it was taken or to return pure gold as a form of returning something better.

Second: It is permissible to repay a gold loan with currency (such as a pound or a dollar) at the rate of the day of repayment, based on the hadith: "There is no harm in taking it at its price on that day, as long as you do not part ways while there is still something between you."

Third: There is no harm if the lender requests the gold to be returned in the same form or something very close to it, if that is available. Otherwise, its value should be returned on the day that an equivalent could not be found.

In summary: The basic principle for repaying a gold loan is to return its equivalent in weight and quality, if possible, or something close to it. It is permissible to agree to repay it in cash at its value on the day of repayment. The borrower may return something better than what was taken without prior request or condition.