Sayyiduna Umar (may Allah be pleased with him) asked about the ruling of the Prophet (peace and blessings be upon him) concerning the fetus. So Sayyiduna Haml bin Malik bin al-Nabighah (may Allah be pleased with him) said: "I had two wives, and they fought. One struck (the other), and the other miscarried, so the Prophet (peace and blessings be upon him) 'ordered a slave for the child, and that the woman be killed for the woman.'"
So he said; then Amr bin Dinar had doubt about it, and what is preserved (mahfuz) is that he ruled her blood money upon the 'aqilah of the woman who killed her.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16410