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.
No references are available.
Ahmad (11343) narrated it, and Ibn Hibban (5889) graded it sahih, via Yunus bin Abu Ishaq, from Abu Wadak Jabr bin Nawf, from Abu Saeed, who mentioned it. See its details in the book Adahi.