Am I sinful for selling my daughter's gold to my friend and then taking it back for a portion of the money, with my friend relinquishing the remainder?

If a person sells something and then regrets it, it is permissible for him to ask for annulment (iqalah), and it is recommended for the buyer to accept it. Scholars differed regarding the annulment of a gold-for-gold or gold-for-cash exchange: is immediate possession (taqabud) a condition for it or not?

1. Shafi'is and Hanbalis: They hold that annulment is a rescission of the contract; therefore, immediate possession is not a condition for it. It is permissible for the parties to a currency exchange to separate before immediate possession takes place.

2. Hanafis and Malikis: They hold that immediate possession is obligatory in annulment. The Malikis consider it a new sale, while the Hanafis consider it a rescission in principle, but a sale with respect to a third party.

The closest opinion is that annulment is a rescission for which immediate possession is not required, provided that it is for the same initial price. However, if it is for more or less, or for a different price, then it is considered a sale, and the conditions of a sale apply to it.

Based on this, what you did by taking back the gold and returning some of the cash is not blameworthy. You are obliged to return the remaining price unless the owner forgives it. However, if you both intended a new sale of the gold, then immediate possession of the gold and cash in the same session would be obligatory, and delaying any part of the price would be forbidden.