Praise be to Allah the Lord of the Worlds.
A Muslim should spend his time in what is beneficial to him in this life and the next. Useful books are countless that one could read a tiny percentage of them throughout his whole life. Therefore, doing so is more useful than wasting time reading books of other religions. This is unless the reader is cultivated enough to easily separate the wheat from the chaff. On the contrary, such a person is urged to do so to further develop his intellectual potentials and broaden his horizons, because this lies in the best interest of his society.
As for the ordinary person who has no knowledge in comparative theology or doesn`t have the needed knowledge in that field, it is prohibited, according to scholars, that he/she reads the books of other religions which contradict the Islamic creed, because he could end up believing in falsehood and rejecting the truth. Kindly refer to {Al-Mosannaf, vol.5/pp.312}.
Ibn Hajar says, "It isn`t permissible for other than a learned man of the faith to read a copy of the Torah which he knows that it has been interpolated or had doubts about it."{Tohfat Al-Mohtaj, 1/178}. Al-Sharwani commented on this in his {Hashyah} by saying, "Al-Zarkhashi and Al-Sobkhi have reported scholarly consensus on this." And Allah the Almighty Knows Best.