Musannaf Ibn Abi Shayba 26:328

'Abbad narrated to us, from 'Umar ibn 'Amir, from Hammad, from Ibrahim, who said: His entire inheritance is for his mother. Meaning the son of the woman who was subjected to *li'an* (imprecation), his maternal relatives are responsible for his blood money (*'aqila*). And likewise is the child of adultery, and the child of a Christian woman whose mother is a Muslim.