Musannaf Ibn Abi Shayba 26:296

Ali ibn Mushir narrated to us, from al-Shaybani, from al-Sha’bi, who said: Ibrahim ibn Yazid had a difference of opinion regarding the son of the woman involved in *li’an* (mutual imprecation). I said: "He is attributed to his mother." Ibrahim said: "He is attributed to his father." So we went to Abdullah ibn Hurmuz, and he wrote for us to the people of Medina, to the family in whose case that had occurred. The reply to their letter came that the Messenger of Allah (peace be upon him) attributed him to his mother.