Sahih al-Bukhari Book 65, Hadith 227
Those who have made their Scripture into parts are the people of the Scripture who divided it into
portions and believed in a part of it and disbelieved the other.
Allah's Messenger (ﷺ) said, "The Um (substance) of the Qur'an is the seven oft-repeated verses (Al- Mathaini) and is the Great Qur'an (i.e. Surat-al-Fatiha).
"As We have sent down (the Scripture) on those who are divided (Jews and Christians)." (15.90) They believed in part of it and disbelieved in the other, (and they) are the Jews and the Christians.