Musannaf Ibn Abi Shayba 18:545

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Hisham ibn ‘Urwah, from his father, from al-Miswar ibn Makhramah, who said: ‘Umar ibn al-Khattab consulted [the people] regarding the *imlas* (miscarriage caused by an assault) of a woman. Al-Mughirah ibn Shu’bah said: I witnessed the Prophet, may Allah bless him and grant him peace, judge regarding it with a *ghurrah* (compensation) of a male slave or a female slave. He said: So ‘Umar said: Bring me someone who will testify with you. So Muhammad ibn Maslamah testified for him.