We were with Ammar when a roasted sheep was brought to him. He said, "Eat."One of the people drew back and said, "I am fasting."Ammar said, "Whoever fasts on the day of doubt has disobeyed Abu al-Qasim ﷺ."
أخبرنا عبد الله بن سعيد الأشج عن أبي خالد عن عمرو بن قيس عن أبي إسحق
كنا عند عمار فأتي بشاة مصلية فقال كلوا فتنحى بعض القوم قال إني صائم فقال عمار من صام اليوم الذي يشك فيه فقد عصى أبا القاسم ﷺ
[Its chain is daif] Tirmidhi narrated it in the Book of Fasting, chapter on the dislike of fasting the day of doubt, no. 686, from Ashaj with this wording, and he said, hasan sahih. It is also in al-Kubra, no. 2498. Ibn Khuzayma and Ibn Hibban and others graded it sahih, and Bukhari mentioned it without a chain in his Sahih, before no. 1906. The hadith has daif corroborating narrations.