What is the source of the law that a child is Jewish only if its mother is Jewish?
The statement that Jewish identity is determined by the mother is found in the Mishnah (Kiddushin 3:12), which says that the child of a gentile woman is like her. The Talmud derives this from the passage in Deut. 7:3-4: “Do not intermarry with [him], do not give your daughter to his son or take his daughter for your son, for he will turn your son from Me”: A child born to your daughter (fathered by a non-Jew) is called “your son”, but a child born to your son (by a non-Jewish mother) is not called “your son”, but “her son”. The Talmud is assuming here that the “he” in Deut.7:4 is your gentile son-in-law, and that “your son” whom “he” will turn away from G-d is your grandson, born to him and to your daughter. The Torah calls that grandson “your son” because he is regarded as Jewish since he had a Jewish mother. In the other case, where a Jewish man marries a gentile woman, the Torah doesn’t speak about the woman’s influence on her children (i.e., it doesn’t say “for she will turn your s
