Musannaf Ibn Abi Shayba 18:558

Abu Bakr narrated to us, he said: Ibn ‘Uyaynah and Waki’ narrated to us, they said: ‘Umar ibn Dharr narrated to us, from Mujahid: That a woman wiped the belly of another woman, and she miscarried. So ‘Umar ibn al-Khattab ordered her to free a slave.