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وَحَدَّثَنَاهُ ابْنُ بَشَّارٍ، وَأَبُو بَكْرِ بْنُ نَافِعٍ جَمِيعًا عَنْ مُحَمَّدِ بْنِ جَعْفَرٍ، عَنْ شُعْبَةَ، عَنْ أَبِي بِشْرٍ، بِهَذَا الإِسْنَادِ وَقَالَ فَسَأَلَهُمْ عَنْ ذَلِكَ، .
This hadith has been narrated by Ibn Bishr with the same chain of transmitters (but with a slight variation) that he (the Holy Prophet) inquired of them (Jews) about it (fasting on the day of ‘Ashura).
USC-MSA web (English) reference