Child of a gentile mother and Jewish father:[1]
A person’s son from a maidservant [i.e., Shifcha Kenanis] or from a Gentile woman [is not considered Jewish and hence] is not liable [for hitting or cursing] his father or mother. [Likewise, this child who is a Gentile is not obligated in the laws of honoring his parents, neither his Jewish father nor Gentile mother. This applies even if the child later converts to Judaism.[2]]
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[1] Michaber 241:8; Rambam Mamrim 5:9
[2] Rabbeinu Yerucham 1:4; Minchas Chinuch Mitzvah 33; Encyclopedia Talmudit Erech Kibud Av Vaeim Vol. 26 p. 409