We were with Ammar on the day of doubt when a roasted sheep was brought, and some of the people moved away from it. Ammar said, "Whoever fasts on this day has disobeyed Abu Qasim ﷺ."
كنا عند عمار في اليوم الذي يشك فيه، فأتى بشاة، فتنحى بعض القوم. فقال عمار: من صام هذا اليوم فقد عصى أبا القاسم ﷺ.
Reported by Abu Dawud (2334), Tirmidhi (686), Nasai (2188), and Ibn Majah (1645), all through various routes from Amr bin Qays Malai, from Abu Ishaq, from Salah bin Zafar, who narrated it. Ibn Khuzayma (1914), Ibn Hibban (3585), and Hakim (1/423) graded it sahih. Tirmidhi said, "It is a hasan sahih hadith." Daraqutni said, "This is a hasan sahih chain, and all its narrators are trustworthy." Hakim said, "It is sahih according to the criteria of the two Shaykhs (Bukhari and Muslim)."Abu Ishaq is Amr bin Abdullah Sabi, whose memory became confused toward the end of his life, but he was not confused in this instance, since there is another route that corroborates it. This is what Ibn Abu Shayba (3/72) reported from Abdul-Aziz bin Abdul-Samad Ammi, from Mansur, from Rubai, that Ammar bin Yasir and some people with him brought them a roasted skinned lamb on a day about which there was doubt whether it was from Ramadan or not from Ramadan. They gathered together, but one man kept apart from them. Ammar said to him, "Come and eat." He said, "I am fasting." Ammar said, "If you believe in Allah and the Last Day, then come and eat." This is a sahih chain.