The Prophet ﷺ said, "The slaughter of the unborn calf is accomplished by the slaughter of its mother."
عن النبي ﷺ قال: ذكاة الجنين ذكاة أمه.
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Imam Ahmad narrated it (11343) from Abu Ubayda, who said, Yunus bin Abu Ishaq told us, from Abu Wadak Jabr bin Nawf, from Abu Saeed, and he related it. Ibn Hibban graded it sahih through this route (5889). Its chain is hasan because of Yunus bin Abu Ishaq Sabi, for he is hasan al-hadith.The hadith has another route, narrated by Abu Dawud (2827), Tirmidhi (1476), Ibn Majah (3199), and Imam Ahmad (11260, 11495), all of them from Mujalid, from Abu Wadak, from Abu Saeed, who related it. In the version of Abu Dawud and Ahmad there is a preceding story, which is that they said, "We said, 'O Messenger of Allah, we slaughter the she-camel and slaughter the cow and the sheep, and we find a fetus in its belly. Should we discard it or eat it?'" He said, "Eat it if you wish, for its slaughtering is the slaughtering of its mother." Tirmidhi said, "A hasan hadith, and it has been narrated through a route other than this one, from Abu Saeed."I say, in its chain is Mujalid, who is Ibn Saeed Hamdani, and he is not strong, and his memory deteriorated in his old age, as stated in Taqrib.It has another route, narrated by Imam Ahmad (11414) from the hadith of Ibn Abu Layla, from Atiya, from Abu Saeed Khudri, similarly. Ibn Abu Layla is Muhammad bin Abdul-Rahman, and Atiya is Ibn Saad Awfi. Both of them are daif due to the poor quality of their memory, but they are usable in corroborating narrations.In sum, the hadith has been narrated through several routes from Abu Saeed Khudri, as Tirmidhi stated, and these routes strengthen one another, and some of them are hasan in their own right.