Hadith 5:2
’Ammar bin Yasir (RAA) narrated, ‘Whoever fasts the day of doubt he has then disobeyed Abu al-Qasim (the Prophet).’ Related by the five Imams, and Ibn Khuzaimah and Ibn Hibban graded it as Sahih
وَعَنْ عَمَّارِ بْنِ يَاسِرٍ - رضى الله عنه - قَالَ: { مَنْ صَامَ اَلْيَوْمَ اَلَّذِي يُشَكُّ فِيهِ فَقَدْ عَصَى أَبَا اَلْقَاسِمِ - صلى الله عليه وسلم -} وَذَكَرَهُ اَلْبُخَارِيُّ تَعْلِيقًا, وَوَصَلَهُ اَلْخَمْسَةُ, وَصَحَّحَهُ اِبْنُ خُزَيْمَةَ, وَابْنُ حِبَّانَ