وَعَنْ عَمَّارِ بْنِ يَاسِرٍ رَضِيَ اللَّهُ عَنْهُمَا
قَالَ: «مَنْ صَامَ الْيَوْمَ الَّذِي يُشَكُّ فِيهِ فَقَدَ عَصَى أَبَا الْقَاسِمِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ»
Ammar ibn Yasir said, “He who fasts on a day about which he is doubtful has disobeyed Abul Qasim”* *i.e., the Prophet (sallallahu alayhi wa sallam). Abu Dawud, Tirmidhi, Nasai.
Mishkat al-Masabih 1887, Book 8, Fasting, Hadith 21. 1 min read