وَ كَتَبَ مُحَمَّدُ بْنُ الْحَسَنِ الصَّفَّارُ رَضِيَ اللَّهُ عَنْهُ إِلَى أَبِي مُحَمَّدٍ الْحَسَنِ بْنِ عَلِيٍّ ع فِي رَجُلٍ مَاتَ وَ عَلَيْهِ قَضَاءٌ مِنْ شَهْرِ رَمَضَانَ عَشَرَةُ أَيَّامٍ وَ لَهُ وَلِيَّانِ هَلْ يَجُوزُ لَهُمَا
English translationBab Ul Qaim Publications
Hadith.2010 - Muhammad ibn al-Hasan al-Saffar, may Allah (swt) be pleased with him, wrote to Imam Abu Muhammad al-Hasan ibn Ali (as): Regarding a man who passed away and had ten days of fasting left from the Month of Ramadan, and he had two heirs. Is it permissible for both heirs to divide the days, with each fasting five days on his behalf? The Imam (as) replied in writing: "The eldest of the two heirs should fast all ten days consecutively, if Allah (swt) wills."
Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.