Hadith #2377 (Sunan Ibn Majah)
Book: The Chapters on Blood Money
Narrator(s): al-Hasan bin 'Ali al-Halwani الحسن بن علي الخلال الحلواني, Bashr bin Thabit al-Basri بشر بن ثابت البصري

he asked the people about the ruling of the Prophet (ﷺ) concerning that – concerning a fetus. Hamal bin Malik bin Nabighah stood up and said: “I was between my two wives and one of them struck the other with a tent-pole, killing her and a fetus. The Messenger of Allah (ﷺ) ruled that the blood money for the fetus was a slave, and that she would be killed in retaliation.”

Source: https://parallelquran.com/hadith/sunan-ibn-majah-2377/