"We were with Ammar bin Yasir when a roasted sheep was brought and he said: 'Eat.' Someone among the people said: 'I am fasting.' So Ammar said: 'Whoever fasts on a day in which there is doubt, then he has disobeyed Abu l-Qasim (ﷺ)."
Reference: Jami` at-Tirmidhi 686 In-book : Book 8, Hadith 5 English translation : Vol. 2, Book 3, Hadith 686
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