وَ رَوَى أَبَانُ بْنُ عُثْمَانَ عَنْ عَبْدِ اَلرَّحْمَنِ بْنِ أَبِي عَبْدِ اَللَّهِ عَنْ أَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ قَالَ: قُلْتُ لَهُ رَجُلٌ أَسَرَتْهُ اَلرُّومُ وَ لَمْ يَصْحُ لَهُ شَهْرُ رَمَضَانَ وَ لَمْ يَدْرِ أَيُّ شَهْرٍ هُوَ قَالَ «يَصُومُ شَهْراً يَتَوَخَّى وَ يَحْسُبُ فَإِنْ كَانَ اَلشَّهْرُ اَلَّذِي صَامَهُ قَبْلَ شَهْرِ رَمَضَانَ لَمْ يُجْزِئْهُ وَ إِنْ كَانَ بَعْدَ شَهْرِ رَمَضَانَ أَجْزَأَهُ ».
Aban ibn Uthman narrated from Abd al-Rahman ibn Abi Abdullah, from Abu Abdullah (a.s): I asked him about a man who was captured by the Romans and did not know when the Month of Ramadan occurred. Imam (a.s) said: "He should fast for a month, making an effort to estimate and calculate. If the month he fasted was before the Month of Ramadan, it does not suffice. However, if it was after the Month of Ramadan, it suffices."