Chapter on Currency Exchange and Its Forms
Man Lā Yaḥḍuruh al-Faqīh|Volume 3|Book 2|Chapter 29
وَ رَوَى أَبَانٌ عَنْ إِسْحَاقَ بْنِ عَمَّارٍ قَالَ: قُلْتُ لِأَبِي إِبْرَاهِيمَ عَلَيْهِ اَلسَّلاَمُ اَلرَّجُلُ يَكُونُ لَهُ عَلَى اَلرَّجُلِ اَلدَّنَانِيرُ فَيَأْخُذُ مِنْهُ دَرَاهِمَ ثُمَّ يَتَغَيَّرُ اَلسِّعْرُ قَالَ "هِيَ لَهُ عَلَى اَلسِّعْرِ اَلَّذِي أَخَذَهَا يَوْمَئِذٍ وَ إِنْ أَخَذَ دَنَانِيرَ وَ لَيْسَ لَهُ دَرَاهِمُ عِنْدَهُ فَدَنَانِيرُهُ عَلَيْهِ يَأْخُذُهَا بِرُءُوسِهَا مَتَى شَاءَ".
Aban narrated from Ishaq ibn Ammar, who said: I asked Abu Ibrahim (Imam Musa ibn Jafar Al-Kadhim عليه السلام) about a man who is owed dinars by another man, but he accepts dirhams instead. Then the price changes. Imam عليه السلام said: "It is based on the value at which he accepted them on that day. However, if he had accepted dinars and not dirhams, then his dinars remain owed to him, and he may take them in their original amount whenever he wishes."
- Ṣaḥīḥ al-Faqīh, p. 247