What is the Gospel that mentioned the coming of Prophet Muhammad (peace be upon him) after Christ, and why do Christians not acknowledge that?

Previous heavenly scriptures—such as the Gospel of Barnabas (Chapter 22), the Book of Isaiah, and Habakkuk—came as heralds of Muhammad, peace be upon him, and his attributes. Although the four Gospels recognized by Christians (Matthew, John, Luke, Mark) have been subjected to human distortion through additions, omissions, and interpretations, the Christians' refusal to acknowledge this stems from ingratitude, obstinacy, concealment of the truth, and envy towards the Prophet, peace be upon him. This is in accordance with the Almighty's saying: "For indeed, it is not you they deny, but it is the verses of Allah that the wrongdoers reject" [Al-An'am: 33], and His saying: "Those to whom We gave the Scripture know him as they know their own sons. But indeed, a party of them conceal the truth while they know" [Al-Baqarah: 146], and His saying: "Many of the People of the Scripture wish they could turn you back to disbelief after your belief, out of envy from themselves, after the truth has become clear to them" [Al-Baqarah: 109].