All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is permissible for you to sell those books for those who make use of it to confirm the truth and refute falsehood, and the money that you earn from it is lawful. But it is forbidden for you to sell it to the general public or to those who use it to propagate falsehood as Allaah Says (what means): {Help you one another in virtue, righteousness and piety but do not help one another in sin and transgression.}[Quran 5:2]
Moreover, Al-Buhooti from the Hanbali school of jurisprudence, said: “It is not permissible to read the books of the People of the Book according to what Imaam Ahmad said because the Prophet got angry when ‘Umar brought to him a copy of the Torah and he said to him: 'Are you in doubt [about the truthfulness of Islam] O Ibn Al-Khattaab.' Also, it is not permissible to read the books of innovators or the books that contain truth mixed with falsehood, and it is not permissible to relate what is written in these books, due to the harm of spoiling the creeds (of their readers).”
This means that it is forbidden to sell them to whoever one fears he will be harmed in his creed. For more benefit, please refer to Fatwa 83344.
Allaah Knows best.