Some men reported that the Messenger of Allah ﷺ said to a man from Aslam after morning had broken on the Day of Ashura, "Go to your people and tell them to fast this day."The man from Aslam asked, "Messenger of Allah, what if I find someone among them who has already eaten?"The Messenger of Allah ﷺ replied, "Let him complete his fast."
عن رجال منهم أن رسول الله ﷺ قال لرجل من أسلم من بعد ما أصبح من يوم عاشوراء: اذهب إلى قومك فمرهم فليصوموا هذا اليوم. قال الأسلمي: يا رسول الله أرأيت إن وجدت أحدا منهم تغدى؟ قال رسول الله ﷺ: فليتم صومه
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Nasai narrated it in Kubra (2871) from Ahmad bin Ibrahim bin Muhammad, who said, Yazid, meaning bin Mawhab, told us, who said, Layth told us, from Aqeel, from Ibn Shihab, from Ibn Sundur, and he related it. Its isnad is hasan because of the shaykh of Nasai, for he is hasan al-hadith. Ibn Sundur is Abdullah bin Sundur Judhami, he and his father both had companionship with the Prophet, and he narrated a story about his father Sundur, "the freedman of Zanbaa Judhami," who is mentioned in the merits of the companions.As for what Abu Dawud narrated (2447) from Muhammad bin Minhal, who said, Yazid bin Zuray told us, from Saeed, from Qatada, from Abdul-Rahman bin Muslama, from his uncle, that the tribe of Aslam came to the Prophet ﷺ and he said, "Have you fasted today?" They said, "No." He said, "Then complete the rest of your day and make it up." In his saying, "and make it up," there is something objectionable. For this reason, Abdul-Haqq said in Ahkam Wusta (245/2), "This hadith is not sound regarding the making up."There is disagreement about this additional wording. Abu Dawud narrated it from the hadith of Yazid bin Zuray, from Saeed, in this manner. But Ahmad (23475) narrated it from Rawh bin Ubada, and Nasai in Kubra (2864) from Bishr, and (2865) from Muhammad bin Bakr, all of them from Saeed bin Abu Aruba, and they did not mention "making up." Likewise, Shuba did not mention it, from Qatada. Tahawi narrated it through his route in Mushkil (2272), as did Ahmad (20329).However, this is complicated by what Bayhaqi (221/4) related through the route of Yazid bin Zuray, from Shuba, in which he mentioned "making up," and he said, Abu Dawud narrated it in Sunan from Muhammad bin Minhal, and likewise Abu Qilaba narrated it from Muhammad bin Minhal, from Yazid, from Shuba. He said, "This occurred in some copies as Saeed. Saeed also narrated it, differing from Shuba in both the isnad and the wording." End of quote.I say, it is as he said. Perhaps the copies of Abu Dawud varied, for the majority of the companions of Saeed bin Abu Aruba did not mention the making up. If this is confirmed, then the disagreement would be over Shuba.In any case, the isnad is daif because of Abdul-Rahman bin Muslama, for he is unknown. There is disagreement about his father's name. It was said, as Abu Dawud said, and it was said he is Ibn Minhal bin Muslama, and it was said Ibn Salama, and other things were said as well. He was known by the kunya Abu Minhal. Only Qatada narrated from him, as Dhahabi said in Mizan. Bayhaqi said in Marifa (361/6), "Unknown, there is disagreement about his father's name, and it is not known who his uncle was." Ibn Qattan said, he is of unknown status. As for Ibn Hibban, he mentioned him in Thiqat, and for this reason Hafiz said of him, "Acceptable," meaning when corroborated. But he was not corroborated on his saying "make it up," so it is an objectionable addition. As for the rest of the hadith, it has sahih supporting narrations.