It was narrated from Abu Dharr that the Prophet (ﷺ) said to a man: "You should fast the thirteenth, fourteenth and fifteenth." (Hasan) Abu 'Abdur-Rahman (An-Nasai) said: This is a mistake, it is not a narration of Bayan; perhaps Sufyan said: "It was narrated to us by two (Ithnan)" and the 'Alif was dropped so it became Bayan.
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا مُحَمَّدُ بْنُ مَنْصُورٍ، عَنْ سُفْيَانَ، عَنْ بَيَانِ بْنِ بِشْرٍ، عَنْ مُوسَى بْنِ طَلْحَةَ، عَنِ ابْنِ الْحَوْتَكِيَّةِ، عَنْ أَبِي ذَرٍّ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ لِرَجُلٍ " عَلَيْكَ بِصِيَامِ ثَلاَثَ عَشْرَةَ وَأَرْبَعَ عَشْرَةَ وَخَمْسَ عَشْرَةَ " . قَالَ أَبُو عَبْدِ الرَّحْمَنِ هَذَا خَطَأٌ لَيْسَ مِنْ حَدِيثِ بَيَانٍ وَلَعَلَّ سُفْيَانَ قَالَ حَدَّثَنَا اثْنَانِ فَسَقَطَ الأَلِفُ فَصَارَ بَيَانٌ .
sunnah.com