What are the revealed books in Islam, and what does believing in them mean?

The Divine Scriptures are the Torah, which was revealed to Musa peace be upon him, Moses, the Zaboor, revealed to Dawood peace be upon him, David, the Injeel or the New Testament, revealed to Eesa peace be upon him, Jesus, and the Qur'an. One of the fundamentals of faith is to firmly believe in the Messages with which Allah sent His Messengers and Prophets to mankind, and to believe that they did convey the message to their respective nations.

Allah destroyed nations who accused their Prophets and Messengers of lying. Therefore, it is our duty to believe in all the Scriptures in general.

What Allah revealed to His Messengers came as the Torah, which was in a written form, sent down to Musa peace be upon him; or as sheets, like those that were sent down to Ibraheem peace be upon him, Abraham; or as verbal revelation, like that which was revealed to Isma'eel peace be upon him, Ishmael, Is'haq peace be upon him, Isaac, or Ya'qoob peace be upon him, Jacob; or as the Qur'an, which was revealed in segments to Allah's Last Prophet ﷺ.

It is incumbent to believe in every word that Allah revealed to His Prophets and Messengers. However, we believe that every later Book abrogates the set of laws of the former one, partially or entirely. Based on this, the Qur'an abrogates many laws that were contained in the Torah and the New Testament.

The Qur'an is the word of Allah and His final Scripture, which He revealed to Muhammad ﷺ to convey it to mankind at large, and it is the principal source of the Islamic Shariah law. Allah sent it down to make manifest everything, and as the means of guidance and mercy to both men and jinn. Since the Qur'an is the last Message which Allah sent to mankind, He has promised to preserve it, saying:

"Verily, it is We Who sent the Qur'an, and We will certainly be preserving it." [Qur'an, al-Hijr 15:9]