عَنْ رَجُلٍ مِنْ بَنِي الْحَارِثِ بْنِ كَعْبٍ، قَالَ: كُنْتُ جَالِسًا عِنْدَ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ فَأَتَاهُ رَجُلٌ فَسَأَلَهُ، فَقَالَ: يَا أَبَا هُرَيْرَةَ! أَنْتَ نَهَيْتَ النَّاسَ أَنْ يَصُومُوا يَوْمَ الْجُمُعَةِ؟ قَالَ: لَا، لَعَمْرُ اللَّهِ! غَيْرَ أَنِّي وَرَبِّ هَذِهِ الْحُرْمَةِ لَقَدْ سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ يَقُولُ: ((لَا يَصُمَنَّ أَحَدُكُمْ يَوْمَ الْجُمُعَةِ إِلَّا فِي أَيَّامٍ يَصُومُهَا فِيهَا))
It is narrated from a member of Banu Harith bin Ka'b, he says: I was sitting with Sayyiduna Abu Hurairah (may Allah be pleased with him), when a man came to him and asked: Abu Hurairah! Have you forbidden people from fasting on Friday? He said: No, by Allah's life! But by the Lord of this sanctity! I heard the Messenger of Allah (peace and blessings be upon him) say: None of you should ever fast on Friday, except that it coincides with days in which he is already fasting.