Musnad Ahmad 28:548

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: 'Amr ibn Shu'ayb mentioned from his father, from his grandfather, who said: "The Messenger of Allah, peace and blessings of Allah be upon him, decreed regarding the blood money (diya) for a fetus while it is in its mother's womb: a ghurra (a slave), either a male slave or a female slave." And he decreed that regarding the wife of Hamal ibn Malik ibn al-Nabigha al-Hudhali. And the Prophet, peace and blessings of Allah be upon him, said: "There is no shighar (a form of marriage exchange) in Islam."