Musannaf Ibn Abi Shayba 9:1503

Abu Bakr narrated to us, he said: Muhammad ibn Fudayl narrated to us, from Mutarrif, from Amir, who said regarding the saying [of Allah]: "And chaste women from those who were given the Scripture before you," he said: The chastity of the Jewess and the Christian woman is that she performs ghusl (full ritual bath) from janabah (major ritual impurity) and that she guards her private part.