Hadith 510440
Chapter 23: Sacrificial Animals - كتاب الضحايا
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، لَمْ يَكُنْ يُضَحِّي عَمَّا فِي بَطْنِ الْمَرْأَةِ . قَالَ مَالِكٌ الضَّحِيَّةُ سُنَّةٌ وَلَيْسَتْ بِوَاجِبَةٍ وَلاَ أُحِبُّ لأَحَدٍ مِمَّنْ قَوِيَ عَلَى ثَمَنِهَا أَنْ يَتْرُكَهَا .
Yahya related to me from Malik from Nafi that Abdullah ibn Umar did not sacrifice for the child in the womb. Malik said, "The sacrifice is sunna, and it is not obligatory. I prefer that anyone who has the price of the animal should not abandon it.''
Reference Muwatta Malik 510440
USC-MSA web (English) reference : Book 23, Hadith 13