He called upon anyone who knew the ruling of the Messenger of Allah ﷺ in such a case. Haml bin Malik then stood up and said, "I was between the rooms of two wives, and one of them struck the other with a tent peg, killing her and her unborn child. The Prophet ﷺ ruled that the blood-money for the unborn child was a male or female slave, and that she be put to death in retaliation."
أخبرنا يوسف بن سعيد قال حدثنا حجاج بن محمد عن ابن جريج قال أخبرني عمرو بن دينار أنه سمع طاوسا يحدث عن ابن عباس
أنه نشد قضاء رسول الله ﷺ في ذلك فقام حمل بن مالك فقال كنت بين حجرتي امرأتين فضربت إحداهما الأخرى بمسطح فقتلتها وجنينها فقضى النبي ﷺ في جنينها بغرة وأن تقتل بها
Reference (isnad): [Its isnad is sahih] Abu Dawud narrated it in the Book of Blood Money, Chapter on the blood money for a fetus, hadith no. 4572, from the hadith of Ibn Jurayj, through this route, and it is in Kubra, hadith no. 6941.