Muwatta Malik, Book 24, Hadith 1053 (In-Book) ⓘ

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."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ كَانَ يَقُولُ إِذَا نُحِرَتِ النَّاقَةُ فَذَكَاةُ مَا فِي بَطْنِهَا فِي ذَكَاتِهَا إِذَا كَانَ قَدْ تَمَّ خَلْقُهُ وَنَبَتَ شَعَرُهُ فَإِذَا خَرَجَ مِنْ بَطْنِ أُمِّهِ ذُبِحَ حَتَّى يَخْرُجَ الدَّمُ مِنْ جَوْفِهِ ‏.‏