Musannaf Ibn Abi Shayba 26:155

Ibn Fudayl narrated to us, from Bassam, from Fudayl, from Ibrahim, regarding a Muslim woman who left behind her Muslim husband and her maternal half-siblings who are Muslims, and she has a son who is a Christian, a Jew, or an infidel. For her husband is half, which is three shares. For her maternal half-siblings is one-third, which is two shares. And what remains is for the agnate (asaba), according to the opinion of Ali and Zayd. A Jew or a Christian does not inherit from a Muslim. Abdullah (Ibn Mas’ud) judged regarding it that the husband has one-fourth, because she has an infidel son. They (the infidel heirs) exclude (others from inheritance) according to the opinion of Abdullah, but they do not inherit. According to the opinion of Ali and Zayd, they neither exclude nor inherit. Abu Bakr said: So this, according to the opinion of Ali and Zayd, is out of six shares, and according to the opinion of Abdullah ibn Mas’ud, it is out of four.