Must the Mukatab accept a better quality of the specified currency?
General Chapter
Al-Mughni
Book of Mukātaba (Contractual Manumission)
Primary text
If the Mukataba is for a specific currency, and the creditor offers currency of the same type but superior in quality, which is generally accepted in commerce where the original currency was to be spent, the Mukatab is obligated to accept it because it constitutes an improvement (ziyada khayr).
Supporting text
If the superior currency is not accepted in some regions where the contracted currency circulates, the Mukatab is not obligated to accept it due to the potential harm (darar) it might cause him.