Musannaf Ibn Abi Shayba 20:58

Abu Bakr narrated to us, he said: Yahya bin Ya'la al-Taymi narrated to us, from Mansur, from Ibrahim, from 'Ubayd bin Nadla, from al-Mughira bin Shu'ba, he said: I witnessed the Messenger of Allah, may Allah bless him and grant him peace, judge regarding it [a case of miscarriage] with a *ghurra* (compensation), a male slave or a female slave. Then 'Ali said to him, "You must bring someone who will testify with you." So Muhammad bin Maslama testified for him.