Maliks Muwatta Book 24, Hadith Number 8.
Section : Slaughtering What is in the Womb of a Slaughtered Animal.
Yahya related to me from Malik from Nafi that Abdullah ibn Umar said, “When a she-camel is slaughtered, what is in its womb is included in the slaughter if it is perfectly formed and its hair has begun to grow. If it comes out of its mother’s womb, it is slaughtered so that blood flows from its heart.”