What is the Quranic verse that proves the distortion of the Gospel, and are the verses that prove its authenticity abrogated, and what is said to Christians who argue for abrogation in the Quran?

There is no doubt that the Torah, the Gospel, and other divine books were revealed by God. This is a core tenet of faith, as Allah Almighty says: "The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have believed in Allah and His angels and His books and His messengers, [saying], 'We make no distinction between any of His messengers.' And they say, 'We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination.'" We believe that distortion occurred in them. Abrogation, however, is firmly established in the Book of Allah and is not a form of distortion; both the abrogating and the abrogated verses are from Allah, and He, glory be to Him, possesses profound wisdom in His legislation. As for distortion, it is an act of humans and a fabrication against Allah. One must be cautious of debating with people of falsehood, except for those who possess deep knowledge.