Question: Is it permissible to examine and study the corrupt books of the disbelievers such as the Torah and the Gospel?
Answer: We do not advise that this be done because the Prophet (sallAllaahu 'alayhi wa sallam) said as is recorded in Saheeh Al-Bukhaaree from the narration of Abu Hurairah: "Do not believe the People of the Book nor disbelieve them, but say: 'We believ in Allaah and in what was revealed to us.'" And in the Musnad of Imaam Ahmad, from the report of Jaabir, the Prophet (sallAllaahu 'alayhi wa sallam) said: "For perhaps you may (end up) either believing in something false or denying something true."
And Allaah says in His Noble Book: "Do you think that they will believe in your Religion even though a party of them used to hear the Word of Allaah and then used to change it knowingly after having understood it?" [Surah Al-Baqarah: 75]
Therefore, I do not advise this. However, it is permissible to do this for a scholar, well established in knowledge, who wants to takes these texts and refute them and expose their errors and contradictions. There is no harm in this.
But he should be well versed in his Islamic Creed, on the subject of Allaah's Names and Attributes and on the Oneness of Allaah in His Worship (Uloohiyyah). His goal should not be to refute those individuals while he himself opposes the Creed of the Muslims.
Shaikh Muqbil bin Haadee Al-Waadi'ee [Tuhfat-ul-Mujeeb: pg. 69-70]