Yahya related to me from Malik from Nafi that Abdullah ibn Umarused to say, "If a she-camel that is being driven as a sacrificialanimal gives birth, the offspring should be carried along as well andthey are sacrificed together with her, and if there is no place wherethey can be carried, they should be carried on the mother until theyare all sacrificed."
USC-MSA web (English) reference: Book 20, Hadith 144
Arabic reference: Book 20, Hadith 847