The Messenger of Allah ﷺ used to enjoin fasting the bright days – the thirteenth, fourteenth and fifteenth (when the moon is full). He said: “It is like fasting for a lifetime.” Another chain from 'Abdul-Malik bin Qatadah bin Malhan Al-Qaisi, from his father, from the Prophet ﷺ with similar wording. Ibn Majah said: Shu'bah erred (in the name of one of the narrators)and Hammam was correct.
عَنْ رَسُولِ اللَّهِ ﷺ أَنَّهُ كَانَ يَأْمُرُ بِصِيَامِ الْبِيضِ ثَلاَثَ عَشْرَةَ وَأَرْبَعَ عَشْرَةَ وَخَمْسَ عَشْرَةَ وَيَقُولُ هُوَ كَصَوْمِ الدَّهْرِ أَوْ كَهَيْئَةِ صَوْمِ الدَّهْرِ حَدَّثَنَا إِسْحَاقُ بْنُ مَنْصُورٍ أَنْبَأَنَا حَبَّانُ بْنُ هِلاَلٍ حَدَّثَنَا هَمَّامٌ عَنْ أَنَسِ بْنِ سِيرِينَ حَدَّثَنِي عَبْدُ الْمَلِكِ بْنُ قَتَادَةَ بْنِ مِلْحَانَ الْقَيْسِيُّ عَنْ أَبِيهِ عَنِ النَّبِيِّ ﷺ نَحْوَهُ قَالَ ابْنُ مَاجَهْ أَخْطَأَ شُعْبَةُ وَأَصَابَ هَمَّامٌ