as I know the Jews holy books are Torah and Talmud .
Torah , speak when some converts to another religion
If thy brother, the son of thy mother, or thy son, or thy daughter, or the wife of thy bosom, or thy friend, which [is] as thine own soul, entice thee secretly, saying,
Let us go and serve other gods, which thou hast not known, thou, nor thy fathers; [Namely], of the gods of the people which [are] round about you, nigh unto thee, or far off from thee, from the [one] end of the earth even unto the [other] end of the earth; Thou shalt not consent unto him, nor hearken unto him;
neither shall thine eye pity him, neither shalt thou spare,
neither shalt thou conceal him: But thou shalt surely kill him; thine hand shall be first upon him to put him to death, and afterwards the hand of all the people. And thou shalt stone him with stones, that he die; because he hath sought to thrust thee away from the LORD thy God, which brought thee out of the land of Egypt, from the house of bondage.
— Deuteronomy 13:6–10[99]
but they also said :
Judaism does not follow the Torah's prescription on this point: there is no punishment today for leaving Judaism.
from : https://en.wikipedia.org/wiki/Apostasy#Judaism