Why do Muslims think that the Injil is corrupt?

In a Nutshell: Muslims believe the Injil to be corrupted due to what the Quran tells us and historic events in the transmission of Isa's (as) life and sayings. Research suggests significant structural changes to his revelation, that should have have been similar to that contained in the Qur'an,. The Injil's corruption is claimed not only by Muslims, but also by Christians who state "the bible has been adapted by 40 authors who have been inspired by holy spirits". What is the Injil? The Injil was the revelation sent down to prophet Isa (Jesus), one of the four revelations recognised by Islam: Torah Zabur Injil Qur'an The word Injil is often used in the Qur'an, the ahadith and early Muslim documents to refer to the revelations made by God to Jesus - it had never been compiled in the form of a literal book, revealed only as an oral book: نَزَّلَ عَلَيْكَ الْكِتَابَ بِالْحَقِّ مُصَدِّقًا لِّمَا بَيْنَ يَدَيْهِ وَأَنزَلَ التَّوْرَاةَ وَالْإِنجِيلَ He has sent down upon you, [O Muhammad], the Book in truth, confirming what was before it. And He revealed the Torah and the Gospel. (Qur'an 3:3) From what the Qur'an tells us, this message was revealed to Isa (as) who went through great hardship to convey it to the Jews. Allah supported him with miracles to evidence his prophethood to his people: Speaking from the cradle Creating birds from clay Healing the blind leaper Power over death Table of food from heaven And so on. Below is an example of a verse from the Qur'an talking about the table of food from the heavens. قَالُوا نُرِيدُ أَن نَّأْكُلَ مِنْهَا وَتَطْمَئِنَّ قُلُوبُنَا وَنَعْلَمَ أَن قَدْ صَدَقْتَنَا وَنَكُونَ عَلَيْهَا مِنَ الشَّاهِدِينَ They said, "We wish to eat from it and let our hearts be reassured and know that you have been truthful to us and be among its witnesses." (Qur'an 5:113) The Injil was revealed to Isa (as) similarly to how the Qur'an was revealed to the Prophet Muhammad (saw):  فَآتَيْنَا الَّذِينَ آمَنُوا مِنْهُمْ أَجْرَهُمْ ۖ وَكَثِيرٌ مِّنْهُمْ فَاسِقُونَ Then We sent following their footsteps Our messengers and followed [them] with Jesus, the son of Mary, and gave him the Gospel. And We placed in the hearts of those who followed him compassion and mercy and monasticism, which they innovated; We did not prescribe it for them except [that they did so] seeking the approval of Allah . But they did not observe it with due observance. So We gave the ones who believed among them their reward, but many of them are defiantly disobedient. (Qur'an 57:27) Is the Injil corrupt? The Injil was a divine message sent by god to Isa (as). The Injil was what Isa (as) would teach the people around him, it was the message he went through so much hardship for. But unfortunately, the Injil itself is no longer available to even Christians who were supposed to preserve it for future generations, to read and act upon. Instead of doing as they were asked, they manipulated the text for their own gain: فَوَيْلٌ لِّلَّذِينَ يَكْتُبُونَ الْكِتَابَ بِأَيْدِيهِمْ ثُمَّ يَقُولُونَ هَٰذَا مِنْ عِندِ اللَّهِ لِيَشْتَرُوا بِهِ ثَمَنًا قَلِيلًا ۖ فَوَيْلٌ لَّهُم مِّمَّا كَتَبَتْ أَيْدِيهِمْ وَوَيْلٌ لَّهُم مِّمَّا يَكْسِبُونَ So, woe to those who write the "scripture" with their own hands, then say, "This is from Allah" to exchange it for a small price. Woe to them for what their hands have written and woe to them for what they earn (Qur'an 2:79) Muslim scholars have argued the Injil refers to a text now lost or hopelessly corrupted. For example, Abdullah Yusuf Ali wrote: "The Injil spoken of by the Qur'an is not the New Testament. It is not the four Gospels now received as canonical. It is the single Gospel which, Islam teaches, was revealed to Jesus, and which he taught. Fragments of it survive in the received canonical Gospels and in some others, of which traces survive (e.g., the Gospel of Childhood or the Nativity, the Gospel of St.Barnabas, etc.)." This is an open secret with bible information websites openly stating over 40 authors inspired by "holy spirits" contributed to the contemporary Bible. https://www.bibleinfo.com/en/questions/who-wrote-the-bible Conclusion The revelation to Isa (as) known as the Injil has not been transmitted faithfully to us - undergoing changes, necessitating yet another messenger, the Prophet Muhammad (saw), to convey the truth.