Salim (may Allah have mercy on him) said: When a man was owed gold or silver by Ibn Umar (may Allah be pleased with them both), he would give him the choice at the time of repayment: "Which of the two kinds do you prefer?" Then he would pay him at the people's rate of exchange, or he would exchange (the money) and then pay him. When the man accepted that, Abdullah (may Allah be pleased with them both) saw no harm in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلح / 11356